Investments and Fair Value Measurements - Summary of Fair Value and Duration of Investments, Including Cash Equivalents, that have been Classified in Gross Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 101,197	$ 247,332
Less than 12 Months, Unrealized Losses	(114)	(690)
More than 12 Months, Fair Value	28,914	24,340
More than 12 Months, Unrealized Losses	(91)	(137)
Total, Fair Value	130,111	271,672
Total, Unrealized Losses	(205)	(827)
U.S. Government and Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	41,474	82,366
Less than 12 Months, Unrealized Losses	(44)	(137)
Total, Fair Value	41,474	82,366
Total, Unrealized Losses	(44)	(137)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	59,274	136,274
Less than 12 Months, Unrealized Losses	(70)	(448)
More than 12 Months, Fair Value	23,079	16,940
More than 12 Months, Unrealized Losses	(78)	(62)
Total, Fair Value	82,353	153,214
Total, Unrealized Losses	(148)	(510)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	214	27,928
Less than 12 Months, Unrealized Losses		(103)
More than 12 Months, Fair Value	5,627	7,131
More than 12 Months, Unrealized Losses	(10)	(71)
Total, Fair Value	5,841	35,059
Total, Unrealized Losses	(10)	(174)
Mortgage-Backed Securities - Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	235	764
Less than 12 Months, Unrealized Losses		(2)
More than 12 Months, Fair Value	208	269
More than 12 Months, Unrealized Losses	(3)	(4)
Total, Fair Value	443	1,033
Total, Unrealized Losses	$ (3)	$ (6)