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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income available to common stockholders									$ 159,139	$ 96,070	$ 81,051
Net income available to common stockholders									$ 159,139	$ 96,070	$ 81,051
Weighted-Average Shares
Net income available to common stockholders (in shares)	49,314,276	49,286,945	49,252,580	49,192,647	49,144,310	48,431,880	42,038,824	40,984,481	49,262,015	45,181,221	40,767,343
Effect of dilutive stock options and warrants (in shares)									208,908	221,757	245,790
Net income available to common stockholders (in shares)	49,511,233	49,492,019	49,451,406	49,427,972	49,379,303	48,643,774	42,243,539	41,220,586	49,470,923	45,402,978	41,013,133
Basic net income per share:
Net income available to common stockholders (in dollars per share)	$ 0.85	$ 0.83	$ 0.80	$ 0.75	$ 0.49	$ 0.50	$ 0.57	$ 0.57	$ 3.23	$ 2.13	$ 1.99
Diluted net income per share:
Net income available to common stockholders (in dollars per share)	$ 0.85	$ 0.83	$ 0.80	$ 0.74	$ 0.49	$ 0.50	$ 0.57	$ 0.56	$ 3.22	$ 2.12	$ 1.98