Fair Value Measurements - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Fair Value Disclosures [Abstract]
Cash and cash equivalents	$ 576,575	$ 665,309	$ 764,034	$ 118,702
Restricted cash and cash equivalents	194,427	187,585
Available-for-sale securities	1,056	3,915
Debt, carrying amount	(854,162)	(864,469)
Forward contracts, carrying amount	(45,453)	(46,912)
Cash and cash equivalents, fair value	576,575	665,309
Restricted cash and cash equivalents, fair value	194,427	187,585
Investments, fair value	1,056	3,915
Debt, fair value	(840,183)	(737,980)
Forward contracts, fair value	$ (45,453)	$ (46,912)