Income Taxes - Income Tax Expense Details (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 expense:
Federal									$ 12	$ (81)	$ (1,622)
State									274	56	(244)
Total current expense									286	(25)	(1,866)
Deferred expense:
Federal									23,395	14,674	38,082
State									(427)	9,738	9,887
Total provision for deferred income taxes									22,968	24,412	47,969
Income Tax Expense (Benefit), Total	$ 5,346	$ 5,545	$ 6,293	$ 6,070	$ (2,125)	$ 11,652	$ 7,214	$ 7,646	$ 23,254	$ 24,387	$ 46,103