Income Taxes - Components of the Consolidated Income Tax Expense (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
Current:
Federal									$ 36,862	$ 33,799	$ 24,394
State									3,791	2,458	2,166
Total current expense									40,653	36,257	26,560
Deferred:
Federal									3,791	44,009	5,439
State									673	380	541
Total deferred expense									4,464	44,389	5,980
Total income tax expense	$ 10,709	$ 15,074	$ 8,384	$ 10,950	$ 36,980	$ 17,457	$ 13,570	$ 12,639	$ 45,117	$ 80,646	$ 32,540