Summary of Investments Classified as Available-For-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 222,619
Gross Unrealized Gains	23	[1]
Gross Unrealized Losses	(149)	[1]
Aggregate Estimated Fair Value	222,493		100,950
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value	16,288		11,012
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value	15,473		4,997
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value	185,725		77,441
Securities of government-sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Estimated Fair Value	5,007		7,500
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	157,268		100,945
Gross Unrealized Gains	17	[1]	20	[1]
Gross Unrealized Losses	(74)	[1]	(15)	[1]
Aggregate Estimated Fair Value	157,211		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	11,511		11,018
Gross Unrealized Gains	1	[1]	1	[1]
Gross Unrealized Losses	(11)	[1]	(7)	[1]
Aggregate Estimated Fair Value	11,501		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	15,476		4,997
Gross Unrealized Gains	2	[1]	0	[1]
Gross Unrealized Losses	(5)	[1]	0	[1]
Aggregate Estimated Fair Value	15,473		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	125,273		77,430
Gross Unrealized Gains	14	[1]	19	[1]
Gross Unrealized Losses	(57)	[1]	(8)	[1]
Aggregate Estimated Fair Value	125,230		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	5,008		7,500
Gross Unrealized Gains	0	[1]	0	[1]
Gross Unrealized Losses	(1)	[1]	0	[1]
Aggregate Estimated Fair Value	5,007		7,500
Long-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	65,351
Gross Unrealized Gains	6	[1]
Gross Unrealized Losses	(75)	[1]
Aggregate Estimated Fair Value	65,282
Long-term investments | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,800
Gross Unrealized Gains	0	[1]
Gross Unrealized Losses	(13)	[1]
Aggregate Estimated Fair Value	4,787
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	60,551
Gross Unrealized Gains	6	[1]
Gross Unrealized Losses	(62)	[1]
Aggregate Estimated Fair Value	$ 60,495
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.