Income Taxes - Schedule of current and deferred 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
Current:
Federal									$ 614	$ 5,868	$ 4,338
State									427	1,163	1,195
Total current									1,041	7,031	5,533
Deferred:
Federal									19,452	(19,441)	(4,980)
State									6,089	(7,229)	(398)
Total deferred									25,541	(26,670)	(5,378)
Total expense (benefit)	$ 27,497	$ 650	$ (13)	$ (1,552)	$ 9,537	$ (30,436)	$ 980	$ 280	$ 26,582	$ (19,639)	$ 155