Cash, Cash Equivalents and Investments - Effective Maturity Dates of Available-for-Sale Investments (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	$ 341,194
1-2 Years	213,098
2-3 Years	92,650
3-4 Years	12,741
4-5 Years	5,846
Fair Value, Total	665,529
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	141,188
1-2 Years	84,007
2-3 Years	77,975
3-4 Years	2,211
4-5 Years	5,759
Fair Value, Total	311,140
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	67,175
1-2 Years	92,280
2-3 Years	0
3-4 Years	0
4-5 Years	0
Fair Value, Total	159,455
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	69,614
1-2 Years	8,957
2-3 Years	7,372
3-4 Years	10,530
4-5 Years	87
Fair Value, Total	96,560
Euro liquidity fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	46,499
1-2 Years	0
2-3 Years	0
3-4 Years	0
4-5 Years	0
Fair Value, Total	46,499
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	2,903
1-2 Years	7,614
2-3 Years	2,725
3-4 Years	0
4-5 Years	0
Fair Value, Total	13,242
Sovereign Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	7,298
1-2 Years	19,007
2-3 Years	4,578
3-4 Years	0
4-5 Years	0
Fair Value, Total	30,883
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	6,517
1-2 Years	1,233
2-3 Years	0
3-4 Years	0
4-5 Years	0
Fair Value, Total	$ 7,750