Summary of Investments Classified as Available-For-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 165,844
Gross Unrealized Gains	10	[1]
Gross Unrealized Losses	(204)	[1]
Aggregate Estimated Fair Value	165,650		100,950
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value	11,217		11,012
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value	19,964		4,997
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value	121,940		77,441
Securities of government-sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value	12,529		7,500
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	114,384		100,945
Gross Unrealized Gains	10	[1]	20	[1]
Gross Unrealized Losses	(64)	[1]	(15)	[1]
Aggregate Estimated Fair Value	114,330		100,950
Short-term investments | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity	1 year		1 year
Amortized Cost	9,791		11,018
Gross Unrealized Gains	1	[1]	1	[1]
Gross Unrealized Losses	(11)	[1]	(7)	[1]
Aggregate Estimated Fair Value	9,781		11,012
Short-term investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity	1 year		1 year
Amortized Cost	19,968		4,997
Gross Unrealized Gains	1	[1]	0	[1]
Gross Unrealized Losses	(5)	[1]	0	[1]
Aggregate Estimated Fair Value	19,964		4,997
Short-term investments | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity	1 year		1 year
Amortized Cost	72,094		77,430
Gross Unrealized Gains	8	[1]	19	[1]
Gross Unrealized Losses	(46)	[1]	(8)	[1]
Aggregate Estimated Fair Value	72,056		77,441
Short-term investments | Securities of government-sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity	1 year		1 year
Amortized Cost	12,531		7,500
Gross Unrealized Gains	0	[1]	0	[1]
Gross Unrealized Losses	(2)	[1]	0	[1]
Aggregate Estimated Fair Value	12,529		7,500
Long-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	51,460
Gross Unrealized Gains	0	[1]
Gross Unrealized Losses	(140)	[1]
Aggregate Estimated Fair Value	51,320
Long-term investments | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,440
Gross Unrealized Gains	0	[1]
Gross Unrealized Losses	(4)	[1]
Aggregate Estimated Fair Value	1,436
Long-term investments | Certificates of deposit | Minimum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity	1 year
Long-term investments | Certificates of deposit | Maximum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity	2 years
Long-term investments | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	50,020
Gross Unrealized Gains	0	[1]
Gross Unrealized Losses	(136)	[1]
Aggregate Estimated Fair Value	$ 49,884
Long-term investments | Corporate debt securities | Minimum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity	1 year
Long-term investments | Corporate debt securities | Maximum
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities contractual maturity	2 years

[1] Unrealized gains and losses are included in other comprehensive loss.