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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 14,177	$ 17,067	$ 17,968	$ 16,172	$ 15,260	$ 16,122	$ 15,160	$ 13,620	$ 65,384	$ 60,162	$ 44,530
Preferred stock dividends											(2,380)
Net income available to common stockholders									$ 65,384	$ 60,162	42,150
Net income available to common stockholders									$ 65,384	$ 60,162	$ 42,150
Weighted-Average Shares
Net income available to common stockholders (in shares)	37,908,873	37,850,827	37,793,448	37,709,883	37,018,014	36,054,867	36,026,763	35,956,436	37,816,399	36,266,356	29,731,420
Effect of dilutive stock options and warrants (in shares)									271,834	288,253	276,960
Net income available to common stockholders (in shares)	38,190,694	38,118,199	38,043,359	38,000,074	37,323,276	36,328,981	36,294,149	36,260,624	38,088,233	36,554,609	30,008,380
Basic net income per share:
Net income available to common stockholders (in dollars per share)	$ 0.37	$ 0.46	$ 0.47	$ 0.43	$ 0.41	$ 0.45	$ 0.42	$ 0.38	$ 1.73	$ 1.66	$ 1.42
Diluted net income per share:
Net income available to common stockholders (in dollars per share)	$ 0.37	$ 0.45	$ 0.47	$ 0.43	$ 0.41	$ 0.45	$ 0.41	$ 0.38	$ 1.72	$ 1.65	$ 1.41