Income Taxes - Carryforward and Valuation allowances (Details) - USD ($)		3 Months Ended	12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tax Cuts and Jobs Act, 2017
Federal income tax rate (as a percent)	21.00%	21.00%	21.00%	35.00%	35.00%
Deferred income tax liabilities due to revalue of net deferred federal tax liabilities		$ 4,531,000
Deferred income tax benefit due to decrease in net deferred income tax liabilities			$ 4,531,000
Uncertain income tax positions
Interest expense recorded			0	$ 0	$ 0
Liability for uncertain income tax matters		$ 0	0	0
State net operating loss carryforward
Operating loss carryforwards
Net operating loss carryforwards			137,913,000
Decrease in valuation allowances			$ 1,286,000	$ 163,000	$ 1,872,000