Derivative Instruments (Narrative) (Details) - USD ($) $ in Thousands	Dec. 30, 2017	Feb. 23, 2017	Dec. 31, 2016	Nov. 30, 2016	Feb. 28, 2015
Derivative [Line Items]
Gain (loss) expected to be reclassified during next 12 months	$ 1,700
Senior unsecured term loan due February 2026
Derivative [Line Items]
Unsecured debt	300,000		$ 300,000
Interest rate swaps
Derivative [Line Items]
Derivative, notional amount	675,000	$ 100,000	$ 575,000
Derivative, fixed interest rate		2.06%
Interest Rate Swap 1
Derivative [Line Items]
Derivative, notional amount				$ 100,000	$ 25,000
Derivative, fixed interest rate				1.615%	1.58%
Interest Rate Swap 1 | Senior unsecured term loan due February 2026
Derivative [Line Items]
Derivative, notional amount	$ 100,000
Derivative, fixed interest rate	1.337%
Interest Rate Swap 2
Derivative [Line Items]
Derivative, notional amount				$ 100,000	$ 50,000
Derivative, fixed interest rate				1.337%	1.975%
Interest Rate Swap 2 | Senior unsecured term loan due February 2026
Derivative [Line Items]
Derivative, notional amount	$ 100,000
Derivative, fixed interest rate	1.615%
Interest Rate Swap 3
Derivative [Line Items]
Derivative, notional amount				$ 230,000
Derivative, fixed interest rate				1.271%
Interest Rate Swap 3 | Senior unsecured term loan due February 2026
Derivative [Line Items]
Derivative, notional amount	$ 100,000
Derivative, fixed interest rate	2.06%
Interest Rate Swap 4
Derivative [Line Items]
Derivative, notional amount				$ 70,000
Derivative, fixed interest rate				1.236%