Discover Financial Services (NYSE:DFS) continues to delight investors: Its shares have returned 16% year-to-date and the credit card company recently released strong third-quarter results, which only added to already high investor interest in this company.

Shares of Discover Financial marked a 52-week high at $65.92 recently, and the company appears to be on track to crush its latest high.

Discover Financial has reported strong earnings throughout the year -- the company recently even achieved record earnings of $1.37 per share, up 14% year over year -- and it doesn't look as if growth is subsiding. In fact, it is continued loan growth, earnings momentum, and high profitability, which could propel Discover Financial's shares even higher in 2015.

Discover Financial is pretty much like any other financial institution: It offers a variety of core banking products such as checking and savings accounts and CDs. The company is also a large player in the lending business: Whether customers need a home equity loan, a traditional mortgage, personal loans or credit cards, Discover Financial provides the solution.

In addition to its deposits and lending business, Discover Financial operates a secure payments network, leading ATM-debit networks, and Diners Club International, which all facilitate cardholders' private and corporate transactions.

Loan growth
For a financial institution, loan growth is key for business growth. The more money Discover Financial can prudently lend out to customers that apply for a home, student, or personal loan, the better for the company.

And Discover Financial has seen some healthy loan growth over the last 12 months: Total loans increased 7.4% to $67.4 billion driven largely by its card segment, which is both a loan driver -- loans were up 6.6% year-over-year, -- as well as the most dominant service line for Discover Financial.

Source: Discover Financial Third Quarter Earnings Presentation

As one can easily see in the chart above, card-related loans are making up the majority of Discover Financial's total ending loan balance of $67.4 billion at the end of the third quarter: 79.7% to be precise.

However, the largest growth rates of 20.9% happened in Discover Financial's personal loan business, which is also one of the most profitable loan categories for the company.

In fact, Discover Financial's credit card and personal loan business are the most profitable for the company with yields consistently at or above 12% in both the most recent quarter as well as in the last year's third quarter.

Source: Discover Financial Third Quarter Earnings Presentation

With a further solidifying economic recovery in the United States, both credit card and personal loan segments could benefit from higher consumer demand, which in turn could translate into further earnings tailwinds for Discover Financial in the coming years.

The Foolish Takeaway
Discover Financial's high reliance on its dominant card business, and attractive growth rates in its high-yielding personal loan business, suggest that the financial services company is well positioned to benefit from cyclical tailwinds and higher loan demand in the years ahead.

Investors have already seen strong year-over-year earnings momentum at Discover Financial, and there are no signs that growth is coming to a halt. If Discover Financial can sustain its loan growth rates throughout a continued recovery in the U.S., higher share prices could very well be the reward for this financial services company and its shareholders.