Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Acadia Healthcare Company Inc (NASDAQ:ACHC) shot nearly 15% higher today after news broke that Acadia would acquire independent British behavioral-health care provider Partnerships in Care (PiC) for $660 million in cash.

So what: PiC is Britain's second-largest independent provider of behavioral health care services, a market which is worth roughly $2 billion and which has been growing by 9% a year over the past decade. PiC operates 23 inpatient facilities with over 1,200 beds in the United Kingdom, and last year the company recorded adjusted EBITDA of approximately $75 million on revenue of roughly $285 million, which has led Acadia to conclude that the acquisition should produce between $0.17 and $0.20 in additional earnings per share for the 2014 fiscal year. That would boost Acadia's expected EPS for the year from an earlier range of $1.26 to $1.29 to a new range of $1.43 to $1.49.

Now what: Acadia has put together strong growth since going public in late 2012 -- its shares have more than doubled, and both revenue (up 85%) and EPS (up 99%) have followed close behind. Acadia isn't cheap at a P/E of over 45, and persistently negative free cash flow is also a concern, but this acquisition helps a growing company diversify internationally without drawing it away from its core competency. I'd be wary of investing in a company that's this highly valued, but growth stocks do earn premiums on the market, and Acadia is poised to put together another year of solid growth with these new resources at its disposal.