Net Impact of Changes in Fair Value of Call Option and Embedded Cash Conversion Option - (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments Gain Loss [Line Items]
Net (loss) gain included in other income, net	$ (8)	$ 70	$ (306)	$ 260
1.25% Call Option [Member]
Derivative Instruments Gain Loss [Line Items]
Net (loss) gain included in other income, net	(2,639)	(10,507)	14,966	(41,710)
1.25% Notes Embedded Cash Conversion Option [Member]
Derivative Instruments Gain Loss [Line Items]
Net (loss) gain included in other income, net	$ 2,631	$ 10,577	$ (15,272)	$ 41,970