Income Taxes - Income tax provision (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal		$ 21,156	$ 26,015	$ 25,515
State		4,477	4,869	4,538
Total current		25,633	30,884	30,053
Deferred:
Charge in federal tax rate due to the 2017 Act		11,375
Federal		(3,193)	(7,748)	(3,634)
State		(1,781)	(646)	(311)
Total deferred		6,401	(8,394)	(3,945)
Total provision for income taxes		$ 32,034	$ 22,490	$ 26,108
Statutory federal rate		35.00%	35.00%	35.00%
Forecast
Deferred:
Statutory federal rate	21.00%