Marketable Securities - Schedule of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 7,234	$ 6,934
Gross Unrealized Gains	0
Gross Unrealized (Losses)	0
Estimated Fair Value	7,234	6,934
Available-for-sale securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	124,204	128,212
Gross Unrealized Gains	21	12
Gross Unrealized (Losses)	0
Estimated Fair Value	124,225	128,224
Money market funds [Member] | Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,234	6,934
Gross Unrealized Gains	0
Gross Unrealized (Losses)	0
Estimated Fair Value	7,234	6,934
U.S. government sponsored entity debt securities [Member] | Available-for-sale securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	116,970	121,278
Gross Unrealized Gains	21	12
Gross Unrealized (Losses)	0
Estimated Fair Value	$ 116,991	$ 121,290