Net Income Per Share - Reconciliation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Net Income	$ 17,968	$ 15,160	$ 34,140	$ 28,780
Diluted net income per share	$ 17,968	$ 15,160	$ 34,140	$ 28,780
Net income available to common stockholders (in shares)	37,793,448	36,026,763	37,751,896	35,991,794
Effect of dilutive stock options and warrants (in shares)	249,911	267,386	270,036	285,754
Net income available to common stockholders (in shares)	38,043,359	36,294,149	38,021,932	36,277,548
Net income available to common stockholders (in dollars per share)	$ 0.47	$ 0.42	$ 0.90	$ 0.80
Net income available to common stockholders (in dollars per share)	$ 0.47	$ 0.41	$ 0.90	$ 0.79