Fair Value Measurements (Carrying value and fair value of debt by hierarchy level) (Details) - USD ($) $ in Thousands	Jul. 01, 2018	Dec. 31, 2017
Secured debt [Member] | Fair value, inputs, level 2 [Member] | Term loan A facility [Member] | Senior Secured Credit Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans payable, fair value disclosure	$ 486,281	$ 502,500
Secured debt [Member] | Fair value, inputs, level 2 [Member] | Revolving credit facility [Member] | Senior Secured Credit Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans payable, fair value disclosure	631,916	598,500
Secured debt [Member] | Fair value, inputs, level 3 [Member] | Term loan A facility [Member] | Senior Secured Credit Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans payable, fair value disclosure	0	0
Secured debt [Member] | Fair value, inputs, level 3 [Member] | Revolving credit facility [Member] | Senior Secured Credit Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans payable, fair value disclosure	0	0
Unsecured debt [Member] | Fair value, inputs, level 2 [Member] | Notes payable, other payables [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable, fair value disclosure	0	0
Unsecured debt [Member] | Fair value, inputs, level 3 [Member] | Notes payable, other payables [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable, fair value disclosure	135	891
Reported value measurement [Member] | Secured debt [Member] | Term loan A facility [Member] | Senior Secured Credit Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	487,500	500,000
Reported value measurement [Member] | Secured debt [Member] | Revolving credit facility [Member] | Senior Secured Credit Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	633,500	600,000
Reported value measurement [Member] | Unsecured debt [Member] | Notes payable, other payables [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 141	$ 904