Net Income Per Share - Reconciliation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income available to common stockholders									$ 81,051	$ 65,384	$ 60,162
Net income available to common stockholders									$ 81,051	$ 65,384	$ 60,162
Weighted-Average Shares
Net income available to common stockholders (in shares)	40,846,650	40,779,423	40,751,720	40,690,573	37,908,873	37,850,827	37,793,448	37,709,883	40,767,343	37,816,399	36,266,356
Effect of dilutive stock options and warrants (in shares)									245,790	271,834	288,253
Net income available to common stockholders (in shares)	41,124,179	41,025,784	40,969,111	40,916,972	38,190,694	38,118,199	38,043,359	38,000,074	41,013,133	38,088,233	36,554,609
Basic net income per share:
Net income available to common stockholders (in dollars per share)	$ 0.55	$ 0.51	$ 0.50	$ 0.43	$ 0.37	$ 0.46	$ 0.47	$ 0.43	$ 1.99	$ 1.73	$ 1.66
Diluted net income per share:
Net income available to common stockholders (in dollars per share)	$ 0.55	$ 0.51	$ 0.49	$ 0.43	$ 0.37	$ 0.45	$ 0.47	$ 0.43	$ 1.98	$ 1.72	$ 1.65