Debt (Revolving Credit Facility Under The Senior Credit Agreement) (Narrative) (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Oct. 13, 2017	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 01, 2018
Line of Credit Facility [Line Items]
Repayments of revolving credit facility			$ 875,000	$ 190,000	$ 895,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			$ 1,000,000
Line of credit facility, commitment fee			0.25%
Revolving credit facility, maturity date			Feb. 05, 2020
Borrowings on the revolving credit facility			$ 525,000
Repayments of revolving credit facility	$ 460,000		875,000
Line of credit facility, outstanding			$ 40,000
Revolving credit facility, effective interest rate			3.48%
Revolving Credit Facility [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Borrowings on the revolving credit facility		$ 55,000
Repayments of revolving credit facility		$ 20,000
Line of credit facility, outstanding						$ 75,000
Minimum [Member] | Revolving Credit Facility [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable interest rate			0.375%
Minimum [Member] | Revolving Credit Facility [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable interest rate			1.375%
Maximum [Member] | Revolving Credit Facility [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable interest rate			1.00%
Maximum [Member] | Revolving Credit Facility [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable interest rate			2.00%