Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Derivative instruments	$ 41,978	$ 69,979
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Fair value of derivative liabilities, Gross amounts	5,355	10,959
Fair value, measurements, recurring [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	2,005,012	345,119
Derivative instruments	41,978	69,979
Total financial assets	4,986,440	831,906
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Fair value of derivative liabilities, Gross amounts	5,355	10,959
Total financial liabilities	5,355	10,959
Fair value, measurements, recurring [Member] | Money market and deposit accounts [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	2,915,170	400,388
Fair value, measurements, recurring [Member] | Publicly traded equity securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	6,461	6,463
Fair value, measurements, recurring [Member] | Certificates of deposit [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	17,819	9,957
Fair value, measurements, recurring [Member] | Level 1 [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	2,005,012	345,119
Derivative instruments	0	0
Total financial assets	4,926,643	751,970
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	2,915,170	400,388
Fair value, measurements, recurring [Member] | Level 1 [Member] | Publicly traded equity securities [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Financial assets	6,461	6,463
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 and cash equivalents	0	0
Derivative instruments	41,978	69,979
Total financial assets	59,797	79,936
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Fair value of derivative liabilities, Gross amounts	5,355	10,959
Total financial liabilities	5,355	10,959
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	$ 17,819	$ 9,957