Derivative Financial Instruments - Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative liabilities, current	$ (407)	$ (7,314)
Derivative liabilities, noncurrent		(3,547)
Interest Rate Swap Contracts \| Derivatives Designated As Hedging Instruments
Derivatives, Fair Value [Line Items]
Derivative assets (liabilities), net, total	36,942	4,760
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	5,826	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	31,523	14,467
Interest Rate Swap Contracts \| Derivatives Designated As Hedging Instruments \| Current Portion Of Other Long-Term Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities, current	$ (407)	(7,314)
Interest Rate Swap Contracts \| Derivatives Designated As Hedging Instruments \| Other Long-Term Liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities, noncurrent		$ (3,547)

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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