Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value disclosure	$ 8,285	$ 69,979
Derivative liability, fair value, gross liability	40,847	10,959
Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, fair value disclosure	985,382	345,119
Derivative assets, fair value disclosure	8,285	69,979
Assets, fair value disclosure	1,458,316	831,906
Derivative liability, fair value, gross liability	40,847	10,959
Fair value, measurements, recurring | Fair value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, fair value disclosure	985,382	345,119
Derivative assets, fair value disclosure	0	0
Assets, fair value disclosure	1,418,680	751,970
Derivative liability, fair value, gross liability	0	0
Fair value, measurements, recurring | Fair value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, fair value disclosure	0	0
Derivative assets, fair value disclosure	8,285	69,979
Assets, fair value disclosure	39,636	79,936
Derivative liability, fair value, gross liability	40,847	10,959
Money market and deposit accounts | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	427,135	400,388
Money market and deposit accounts | Fair value, measurements, recurring | Fair value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	427,135	400,388
Money market and deposit accounts | Fair value, measurements, recurring | Fair value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	0	0
Publicly traded equity securities | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	6,163	6,463
Publicly traded equity securities | Fair value, measurements, recurring | Fair value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	6,163	6,463
Publicly traded equity securities | Fair value, measurements, recurring | Fair value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	0	0
Certificates of deposit | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	31,351	9,957
Certificates of deposit | Fair value, measurements, recurring | Fair value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	0	0
Certificates of deposit | Fair value, measurements, recurring | Fair value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value disclosure	$ 31,351	$ 9,957