Fair Value Measurements And Derivative Instruments (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Debt instrument, face amount	$ 975,000,000		$ 975,000,000
Unrealized gain (loss) recognized in accumulated other comprehensive income	467,000	$ 153,000	(772,000)	$ (68,000)
Unrealized gain (loss) reclassified from accumulated other comprehensive income to interest expense	144,000	$ 110,000	424,000	$ 428,000
Gain (loss) to be reclassified to interest expense during next 12 months	65,000		65,000
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Derivatives, Fair Value [Line Items]
Carrying value and estimated fair value of debt	1,083,178,000		1,083,178,000		$ 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	$ 1,061,598,000		$ 1,061,598,000		$ 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