Indebtedness - Future Principal Payments (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Debt Disclosure [Abstract]
2018	$ 3,672
2019	931,541
2020	338,433
2021	14,420
2022	575,518
Thereafter	399,563
Total	2,263,147
Unamortized premiums, discounts and certain issuance costs	18,055
Total debt outstanding	$ 2,245,092

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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