Derivative Held for Hedging the Risk of Changes in Forecasted Interest Payments on Issuance of Long-term Debt (Details) - USD ($)				12 Months Ended
		Aug. 08, 2016	Aug. 05, 2016	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Fair Value Deferred in AOCI		$ 1,000,000	$ 1,000,000
April/2012
Derivative Instruments, Gain (Loss) [Line Items]
Terminated				2012-04
Description				Treasury lock
Aggregate Notional Amount				$ 500,000,000
Fair Value When Terminated				(3,137,000)
Fair Value Deferred in AOCI	[1]			2,510,000
Ineffective Portion at Termination				$ 627,000
September/2016
Derivative Instruments, Gain (Loss) [Line Items]
Terminated				2016-09
Description				Treasury lock
Aggregate Notional Amount				$ 200,000,000
Fair Value When Terminated				1,298,000
Fair Value Deferred in AOCI	[1]			$ (1,298,000)
September/2016
Derivative Instruments, Gain (Loss) [Line Items]
Terminated				2016-09
Description				Treasury lock
Aggregate Notional Amount				$ 150,000,000
Fair Value When Terminated				(323,000)
Fair Value Deferred in AOCI	[1]			215,000
Ineffective Portion at Termination				$ 108,000

[1] The amount reported in AOCI will be reclassified to interest expense as interest payments are made on the related notes.