Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Jan. 01, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment from adoption of new accounting standard			$ 269,776		$ 1,123
Assets:
Publicly traded equity securities	$ 1,717			$ 6,163
Derivative instruments	73,074			8,285
Liabilities:
Derivative instruments	9,740			40,847
Fair value, measurements, recurring
Assets:
Publicly traded equity securities	1,717			6,163
Derivative instruments	73,074			8,285
Assets	683,780			1,458,316
Liabilities:
Derivative instruments	9,740			40,847
Fair value, measurements, recurring | Cash
Assets:
Cash and cash equivalents	486,648			985,382
Fair value, measurements, recurring | Money market and deposit accounts
Assets:
Cash and cash equivalents	119,518			427,135
Fair value, measurements, recurring | Certificates of deposit
Assets:
Cash and cash equivalents	2,823			31,351
Fair value, measurements, recurring | Fair value, Inputs, Level 1
Assets:
Publicly traded equity securities	1,717			6,163
Derivative instruments	0			0
Assets	607,883			1,418,680
Liabilities:
Derivative instruments	0			0
Fair value, measurements, recurring | Fair value, Inputs, Level 1 | Cash
Assets:
Cash and cash equivalents	486,648			985,382
Fair value, measurements, recurring | Fair value, Inputs, Level 1 | Money market and deposit accounts
Assets:
Cash and cash equivalents	119,518			427,135
Fair value, measurements, recurring | Fair value, Inputs, Level 1 | Certificates of deposit
Assets:
Cash and cash equivalents	0			0
Fair value, measurements, recurring | Fair value, Inputs, Level 2
Assets:
Publicly traded equity securities	0			0
Derivative instruments	73,074			8,285
Assets	75,897			39,636
Liabilities:
Derivative instruments	9,740			40,847
Fair value, measurements, recurring | Fair value, Inputs, Level 2 | Cash
Assets:
Cash and cash equivalents	0			0
Fair value, measurements, recurring | Fair value, Inputs, Level 2 | Money market and deposit accounts
Assets:
Cash and cash equivalents	0			0
Fair value, measurements, recurring | Fair value, Inputs, Level 2 | Certificates of deposit
Assets:
Cash and cash equivalents	$ 2,823			$ 31,351
Accounting Standards Update 2016-01
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment from adoption of new accounting standard		$ 2,100
Retained Earnings (Accumulated Deficit)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment from adoption of new accounting standard			271,900		$ 1,123
Retained Earnings (Accumulated Deficit) | Accounting Standards Update 2016-01
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustment from adoption of new accounting standard			$ 2,100