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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net Income
Net income available to common stockholders	$ 20,006	$ 17,968	$ 37,699	$ 34,140
Diluted net income per share	$ 20,006	$ 17,968	$ 37,699	$ 34,140
Weighted-Average Shares
Net income available to common stockholders (in shares)	40,751,720	37,793,448	40,721,147	37,751,896
Effect of dilutive stock options and warrants (in shares)	217,391	249,911	220,338	270,036
Diluted net income per share (in shares)	40,969,111	38,043,359	40,941,485	38,021,932
Per Share Amount
Net income available to common stockholders (in dollars per share)	$ 0.50	$ 0.47	$ 0.93	$ 0.90
Diluted net income per share (in dollars per share)	$ 0.49	$ 0.47	$ 0.92	$ 0.90