Ever the steady creator of shareholder value, Markel Corporation (NYSE:MKL) is set to report third-quarter results on Wednesday. And while it's not generally one to offer big surprises around earnings season, this provides a great opportunity for long-term investors to smile at a snapshot of what their favorite specialty insurer and financial holding company has accomplished.

For perspective, consensus estimates call for Markel's revenue to rise slightly year over year to $1.31 billion, and translate to 21.1% growth in earnings per share to $6.26.

On book value, investment results
But more importantly, Markel generally kicks off each quarterly report by offering a look at changes in book value per share, growth of which is arguably the most useful metric to gauge its success as a diversified financial holding company. By the end of last quarter, book value per share had increased 2% from the start of the year, but also decreased 1.7% sequentially from the prior quarter to $554.97. However, that decline was the result of a decrease in fair value of Markel's fixed maturity portfolio, which itself was due to increasing interest rates so far in 2015. And because Markel has no intention of selling before maturity, this net unrealized investment loss should fade in future quarters.

Speaking of which, Markel will also provide a snapshot of its overall investment portfolio, including gains or declines in net investment income (up 1.7% last quarter to $90.6 million), net unrealized gains ($1.7 billion last quarter), total invested assets ($18.5 billion at the end of Q2), and how much of that total is comprised of equity securities (24% in Q2, or $4.4 billion). 

On the insurance side
Next, Markel will provide updates on the underwriting results of its insurance businesses. Last quarter, it achieved a consolidated combined ratio of 96%, which means it earned $4 for every $100 in premiums it wrote. That consolidated combined ratio will include results from Markel's U.S. insurance segment (93% last quarter), international insurance (98% last quarter), and reinsurance (100% last quarter).

On a related note, expect commentary on its acquisition of CATCo Investment Management during the quarter. CATCo, for its part, manages around $2.7 billion of retrocession and traditional reinsurance portfolios for clients around the world, and its existing management team will effectively continue their work under the wing of Markel going forward.

In any case, don't expect Markel to write unprofitable business if it can help it. "We continue to exercise a disciplined underwriting approach," reminded CEO Alan Kirshner last quarter, "and will only write business that supports our underwriting profit targets."

On the non-insurance side
Finally, look for updates on the performance and future direction of Markel's growing group of non-insurance businesses, which fall under the umbrella of Markel Ventures.

Operating revenue at Ventures last quarter grew 30.4% year over year to $239.6 million, with growth driven mostly by Markel's purchase of auto-transport trailer maker Cottrell last year. But because Cottrell had performed so well through the first half of the year -- and because a portion of that purchase was based on post-acquisition sales through the end of 2015 -- Markel had to increase its contingent consideration obligation by $17.6 million in Q2, translating to a net loss of $2.6 million from Markel Ventures during the quarter. Still, it's an enviable problem to have an acquired business performing significantly better than expectations, so you'll be hard-pressed to find a long-term-oriented investor willing to complain if Cottrell repeats its outperformance again in Q3.

Steve Symington owns shares of Markel. The Motley Fool owns shares of and recommends Markel. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.