Cash, Cash Equivalents and Investments - Components of Cash, Cash Equivalents and Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Cash	$ 77,307	$ 45,951
Money market instruments	2,334	6,024
Cash and cash equivalents	79,641	51,975	$ 55,694	$ 40,644
Short-term investments	341,194	296,468
Limited partnership interest (accounted for using cost method)	0	942
Long-term investments	324,335	273,088
Total	745,170	621,531
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	67,175	109,360
Long-term investments	92,280	44,437
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	69,614	61,994
Long-term investments	26,946	24,582
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	141,188	54,376
Long-term investments	169,952	176,575
Euro liquidity fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	46,499	47,730
Sovereign Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	7,298	21,440
Long-term investments	23,585	13,503
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	2,903	978
Long-term investments	10,339	8,180
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments	6,517	590
Long-term investments	$ 1,233	$ 4,869