Income Taxes - Income Tax Expense (Benefit) (Details) - USD ($) $ 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
Federal
Current									$ 13,616	$ 32,282	$ 24,521
Deferred									3,517	13,980	665
Total Federal									17,133	46,262	25,186
State
Current									720	323	248
Deferred									(8)	(148)	(129)
Total State									712	175	119
Total Federal and State	$ 4,952	$ 2,876	$ 4,010	$ 6,007	$ 22,255	$ 8,883	$ 8,604	$ 6,695	$ 17,845	$ 46,437	$ 25,305