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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net Income
Net income available to common stockholders	$ 24,136	$ 20,006	$ 47,329	$ 37,699
Diluted net income per share	$ 24,136	$ 20,006	$ 47,329	$ 37,699
Weighted-Average Shares
Net income available to common stockholders (in shares)	42,038,824	40,751,720	41,514,565	40,721,147
Effect of potentially dilutive stock options and restricted stock awards (in shares)	204,715	217,391	220,456	220,338
Diluted net income per share (in shares)	42,243,539	40,969,111	41,735,021	40,941,485
Per Share Amount
Net income available to common stockholders (in dollars per share)	$ 0.57	$ 0.50	$ 1.14	$ 0.93
Diluted net income per share (in dollars per share)	$ 0.57	$ 0.49	$ 1.13	$ 0.92