Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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

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The noncurrent cash, cash equivalents and investments that is restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits classified as long-term; that is not expected to be released from such existing restrictions within one year of the balance sheet date or operating cycle, whichever is longer. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. Includes noncurrent cash equivalents and investments that are similarly restricted as to withdrawal, usage or disposal.

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Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, at carrying value	$ 112,653	$ 85,909	$ 51,777	$ 161,558
Restricted cash	59,703	71,708
Current maturities of long-term debt	(3,375)	(31,676)
Long-term debt	(1,022,004)	(1,030,205)
Carrying Amount \| Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, at carrying value	112,653	85,909
Restricted cash	59,703	71,708
Current maturities of long-term debt	(3,375)	(31,676)
Long-term debt	(1,022,004)	(1,030,205)
Carrying Amount \| Fair Value, Measurements, Recurring \| Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps, assets	15,440
Interest rate swaps, liabilities		11,225
Carrying Amount \| Fair Value, Measurements, Recurring \| Foreign currency exchange contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign currency option contracts	2,807	464
Carrying Amount \| Fair Value, Measurements, Recurring \| Foreign currency option contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign currency option contracts	352	391
Fair Value \| Level 1 \| Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	112,653	85,909
Restricted cash	59,703	71,708
Current maturities of long-term debt	0	0
Long-term debt	0	0
Fair Value \| Level 1 \| Fair Value, Measurements, Recurring \| Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps, assets	0
Interest rate swaps, liabilities		0
Fair Value \| Level 1 \| Fair Value, Measurements, Recurring \| Foreign currency exchange contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign currency option contracts	0	0
Fair Value \| Level 1 \| Fair Value, Measurements, Recurring \| Foreign currency option contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign currency option contracts	0	0
Fair Value \| Level 2 \| Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current maturities of long-term debt	(3,375)	(31,984)
Long-term debt	(1,030,135)	(1,030,708)
Fair Value \| Level 2 \| Fair Value, Measurements, Recurring \| Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps, assets	15,440
Interest rate swaps, liabilities		11,225
Fair Value \| Level 2 \| Fair Value, Measurements, Recurring \| Foreign currency exchange contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign currency option contracts	2,807	464
Fair Value \| Level 2 \| Fair Value, Measurements, Recurring \| Foreign currency option contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign currency option contracts	$ 352	$ 391