Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative instruments	$ 8,985	$ 8,285
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Fair value of derivative liabilities, Gross amounts	39,984	40,847
Fair value, measurements, recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash	1,639,586	985,382
Derivative instruments	8,985	8,285
Total financial assets	2,071,999	1,458,316
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Fair value of derivative liabilities, Gross amounts	39,984	40,847
Total financial liabilities	39,984	40,847
Fair value, measurements, recurring [Member] \| Money market and deposit accounts [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	384,222	427,135
Fair value, measurements, recurring [Member] \| Publicly traded equity securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	6,755	6,163
Fair value, measurements, recurring [Member] \| Certificates of deposit [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	32,451	31,351
Fair value, measurements, recurring [Member] \| Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash	1,639,586	985,382
Derivative instruments	0	0
Total financial assets	2,030,563	1,418,680
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Fair value of derivative liabilities, Gross amounts	0	0
Total financial liabilities	0	0
Fair value, measurements, recurring [Member] \| Level 1 [Member] \| Money market and deposit accounts [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	384,222	427,135
Fair value, measurements, recurring [Member] \| Level 1 [Member] \| Publicly traded equity securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	6,755	6,163
Fair value, measurements, recurring [Member] \| Level 1 [Member] \| Certificates of deposit [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	0	0
Fair value, measurements, recurring [Member] \| Level 2 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash	0	0
Derivative instruments	8,985	8,285
Total financial assets	41,436	39,636
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Fair value of derivative liabilities, Gross amounts	39,984	40,847
Total financial liabilities	39,984	40,847
Fair value, measurements, recurring [Member] \| Level 2 [Member] \| Money market and deposit accounts [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	0	0
Fair value, measurements, recurring [Member] \| Level 2 [Member] \| Publicly traded equity securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	0	0
Fair value, measurements, recurring [Member] \| Level 2 [Member] \| Certificates of deposit [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	32,451	$ 31,351
ASU 2016-01 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative effect on retained earnings	$ 2,100

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Fair value portion 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.

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- Definition

Amount of the cumulative effect on retained earnings net of related income tax effect.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

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Fair value, before 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. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
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-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=SL51823488-111719

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Fair value, before effects of master netting arrangements, of a financial liability or 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. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
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