Income Taxes - Total income tax provision (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current income tax provision:
Federal									$ 16,928	$ 12,460	$ 9,628
State									4,655	4,144	3,466
Total current income tax provision									21,583	16,604	13,094
Deferred income tax provision (benefit):
Federal									2,379	(887)	(1,789)
State									1,253	(508)	(586)
Total deferred income tax provision (benefit)									3,632	(1,395)	(2,375)
Total income tax provision	$ 7,238	$ 5,877	$ 6,358	$ 5,742	$ 4,750	$ 4,801	$ 4,601	$ 1,056	$ 25,215	$ 15,209	$ 10,719