Basis of Presentation and Summary of Significant Accounting Policies - Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Carrying Amount
Summary of the fair value and carrying value of debt
Total debt	$ 2,075,904	$ 2,026,902
Carrying Amount | Fixed rate debt
Summary of the fair value and carrying value of debt
Total debt	1,041,904	1,041,402
Carrying Amount | Floating rate debt
Summary of the fair value and carrying value of debt
Total debt	1,034,000	985,500
Fair Value
Summary of the fair value and carrying value of debt
Total debt	1,963,000	1,946,000
Fair Value | Fixed rate debt
Summary of the fair value and carrying value of debt
Total debt	928,000	960,000
Fair Value | Floating rate debt
Summary of the fair value and carrying value of debt
Total debt	$ 1,035,000	$ 986,000