Income Taxes - Components (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax payable
Federal									$ 21,413	$ 18,627	$ 15,022
State									3,479	4,477	3,293
Deferred tax payable
Federal									(2,627)	(441)	604
State									212	(995)	(121)
Income tax expense	$ 1,330	$ 6,445	$ 9,091	$ 5,611	$ 5,728	$ 7,587	$ 4,986	$ 3,367	$ 22,477	$ 21,668	$ 18,798
Effective tax rate									29.10%	39.50%	39.80%