Fair Value Measurements And Derivative Instruments (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Debt instrument, face amount	$ 960,520,000		$ 960,520,000
Unrealized gain (loss) recognized in accumulated other comprehensive income	(1,309,000)	$ 16,000	(1,239,000)	$ (221,000)
Unrealized gain (loss) reclassified from accumulated other comprehensive income to interest expense	130,000	$ 140,000	280,000	$ 319,000
Gain (loss) to be reclassified to interest expense during next 12 months	40,000		40,000
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Derivatives, Fair Value [Line Items]
Carrying value and estimated fair value of debt	1,070,194,000		1,070,194,000		$ 1,103,327,000
Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives, Fair Value [Line Items]
Carrying value and estimated fair value of debt	$ 1,060,331,000		$ 1,060,331,000		$ 1,098,248,000
Interest Rate Swap: $200,000 Third Term Loan [Member]
Derivatives, Fair Value [Line Items]
Fixed interest payment, percentage	3.894%		3.894%
Notional amount	$ 50,000,000		$ 50,000,000
Maturity Date			Oct. 03, 2019