Debt (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 28, 2017	Jul. 31, 2016	Feb. 29, 2016
Debt Instrument [Line Items]
Repayments of Long-term Lines of Credit	$ (325,123)	$ (7,475)	$ (14,736)
Revolving Credit Facility, Interest Payable Monthly At Floating Rate, Due December 2017 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		600,000
Aggregate principal amount of term loan		$ 325,000
Revolving credit facility interest payable monthly at floating rate due December 2019 [Member}
Debt Instrument [Line Items]
Line of Credit Facility Accordian Feature				$ 100,000
Term Loan A, Amount Outstanding	0
Line of Credit Facility, Maximum Borrowing Capacity				$ 300,000	$ 400,000	$ 470,300
Unsecured Senior Notes Due 2019 [Member]
Debt Instrument [Line Items]
Senior Notes	$ 500,000
Stated interest rate on unsecured senior notes	6.375%
Unsecured Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Senior Notes	$ 800,000
Stated interest rate on unsecured senior notes	7.125%