Indebtedness - Principal Repayment (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Required principal payments under outstanding debt
2017	$ 0
2018	541,000
2019	400,000
2020	0
2021	400,000
Thereafter	1,858,478
Total principal payments	3,199,478
Convertible senior unsecured notes	8,478	$ 8,478
Convertible senior notes, due 2027 at 3.8%
Required principal payments under outstanding debt
Convertible senior unsecured notes	$ 8,478

Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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