Marketable Securities - Summary of Marketable Securities Designated as Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Marketable Securities [Line Items]
Amortized Cost	$ 196,817	$ 127,432
Gross Unrealized Gains	4	2
Gross Unrealized Losses	(347)	(129)
Estimated Fair Value	196,474	127,305
Corporate bonds
Schedule Of Marketable Securities [Line Items]
Amortized Cost	125,132	99,592
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(304)	(119)
Estimated Fair Value	124,829	99,474
Municipal bonds
Schedule Of Marketable Securities [Line Items]
Amortized Cost	16,228	18,146
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(6)	(10)
Estimated Fair Value	16,224	18,137
Commercial paper
Schedule Of Marketable Securities [Line Items]
Amortized Cost	37,236	9,196
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	37,236	9,196
Government securities
Schedule Of Marketable Securities [Line Items]
Amortized Cost	8,704
Gross Unrealized Gains	1
Gross Unrealized Losses	(17)
Estimated Fair Value	8,688
Agency securities
Schedule Of Marketable Securities [Line Items]
Amortized Cost	7,273
Gross Unrealized Gains	0
Gross Unrealized Losses	(20)
Estimated Fair Value	7,253
Certificates of deposit
Schedule Of Marketable Securities [Line Items]
Amortized Cost	2,244	498
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 2,244	$ 498