Long-term Debt Unused Borrowing Capacity (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	May. 27, 2014
Line of Credit Facility [Line Items]
Long-term debt	$ 2,180,847	$ 1,603,772
Second Amended and Restated Senior Secured Syndicated Credit Facility Agreement [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	625,000
Long-term debt	44,812
Debt Instrument, Unused Borrowing Capacity, Amount	575,653
Second Amended and Restated Senior Secured Syndicated Credit Facility Agreement [Member] | Letter of credit guarantees [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	$ 4,535
Prior Credit Agreement [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		625,000	$ 625,000
Long-term debt		43,187
Debt Instrument, Unused Borrowing Capacity, Amount		579,175
Prior Credit Agreement [Member] | Letter of credit guarantees [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount		$ 2,638