Income Taxes Income Tax Eff Rate Recon (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
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent									35.00%
Pretax income	$ 21,692	$ 6,974	$ 2,505	$ 1,360	$ 22,080	$ 9,042	$ 3,939	$ (1,111)	$ 32,531	$ 33,950	$ 33,911
Provision for income taxes at federal statutory rate									(11,386)	(11,883)	(11,869)
Tax rate change									(3,190)	0	0
State income taxes, net of federal benefit									(1,860)	(1,977)	(1,979)
Manufacturing deduction									958	1,142	1,274
Other									88	(306)	41
Provision for income taxes									$ (15,390)	$ (13,024)	$ (12,533)
Effective tax rate									47.30%	38.40%	37.00%
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent									21.00%