Derivative Financial Instruments - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative liabilities, current	$ (7,314)	$ (16,533)
Derivative liabilities, noncurrent	(3,547)	(14,456)
Derivatives Designated As Hedging Instruments | Current Portion Of Other Long-Term Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities, current	(7,314)
Interest Rate Swap Contracts | Derivatives Designated As Hedging Instruments
Derivatives, Fair Value [Line Items]
Derivative assets (liabilities), net, total	4,760	(16,852)
Interest Rate Swap Contracts | Derivatives Designated As Hedging Instruments | Prepaid expenses, deferred costs, and other current assets
Derivatives, Fair Value [Line Items]
Derivative assets, current	1,154
Interest Rate Swap Contracts | Derivatives Designated As Hedging Instruments | Prepaid expenses, deferred costs, and other noncurrent assets
Derivatives, Fair Value [Line Items]
Derivative assets, noncurrent	14,467	14,137
Interest Rate Swap Contracts | Derivatives Designated As Hedging Instruments | Current Portion Of Other Long-Term Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities, current		(16,533)
Interest Rate Swap Contracts | Derivatives Designated As Hedging Instruments | Other Long-Term Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities, noncurrent	(3,547)	$ (14,456)
Foreign Exchange Contract | Derivatives Designated As Hedging Instruments | Current portion of long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities, noncurrent	$ (100)