Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments		$ 50,000
Total assets	$ 17,451,692	15,841,258
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	1,178,986	594,946
Short-term investments		50,000
Derivative contracts	6,455	479
Total assets	1,185,441	645,425
Derivative contracts	(9,000)	(8,531)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	1,178,986	594,946
Short-term investments		50,000
Total assets	1,178,986	644,946
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative contracts	6,455	479
Total assets	6,455	479
Derivative contracts	$ (9,000)	$ (8,531)