Income Taxes - A Reconciliation of the Provision for income taxes from continuing operations (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
Income Tax Disclosure [Abstract]
Expected provision at federal statutory rate									$ 18,465	$ 15,651	$ 13,446
State income taxes, net									1,612	1,672	1,714
Change in valuation allowance									(578)	(718)	(2,385)
Domestic production activity deduction									(957)	(1,247)	(1,002)
Share-based compensation									(4,254)	(1,408)
Compensation limits									931	0	0
Federal and state tax credits									(1,058)	(1,065)	0
Tax benefit from the Tax Act									(3,343)	0	0
Other									117	648	454
Total	$ (2,357)	$ 7,491	$ 2,947	$ 2,854	$ 3,775	$ 2,316	$ 3,570	$ 3,872	$ 10,935	$ 13,533	$ 12,227
Effective tax rate									20.70%	30.30%	31.80%