Fair Value Measurements Non-Recurring Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2018	Oct. 01, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Impairment of Long-Lived Assets Held-for-use	$ 118	$ 928	$ 1,886	$ 1,146
Impairment of Long-Lived Assets to be Disposed of	229	$ 113	270	$ 658
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Assets Held and Used, Long Lived, Fair Value Disclosure	226		226		$ 757
Assets Held-for-sale, Long Lived, Fair Value Disclosure	1,115		1,115		1,560
Total	1,341		1,341		2,317
Fair Value, Measurements, Nonrecurring | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Assets Held and Used, Long Lived, Fair Value Disclosure	0		0		0
Assets Held-for-sale, Long Lived, Fair Value Disclosure	0		0		0
Total	0		0		0
Fair Value, Measurements, Nonrecurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Assets Held and Used, Long Lived, Fair Value Disclosure	0		0		0
Assets Held-for-sale, Long Lived, Fair Value Disclosure	0		0		0
Total	0		0		0
Fair Value, Measurements, Nonrecurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis
Assets Held and Used, Long Lived, Fair Value Disclosure	226		226		757
Assets Held-for-sale, Long Lived, Fair Value Disclosure	1,115		1,115		1,560
Total	$ 1,341		$ 1,341		$ 2,317