Cash Cash Equivalents and Short-term Investments (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents held by third party	$ 721	$ 500
Schedule of Available-for-sale Securities [Line Items]
Total cash and cash equivalents, Amortized Cost	98,922	170,132	174,674	76,568
Total short-term investments, Amortized Cost	124,980	104,845
Total short-term investments, Unrealized Gains	152	194
Total short-term investments, Unrealized Losses	(131)	(38)
Total short-term investments	125,001	105,001
Cash, cash equivalents and short-term investments, Amortized Cost	223,902	274,977
Cash, cash equivalents and short-term investments, Unrealized Gains	152	194
Cash, cash equivalents and short-term investments, Unrealized Losses	(131)	(38)
Cash, cash equivalents and short-term investments, Estimated Fair Value	223,923	275,133
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Total short-term investments, Amortized Cost	47,938	40,503
Total short-term investments, Unrealized Gains	60	90
Total short-term investments, Unrealized Losses	(54)	(10)
Total short-term investments	47,944	40,583
U.S. agency securities
Schedule of Available-for-sale Securities [Line Items]
Total short-term investments, Amortized Cost	39,267	31,720
Total short-term investments, Unrealized Gains	36	40
Total short-term investments, Unrealized Losses	(26)	(13)
Total short-term investments	39,277	31,747
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Total short-term investments, Amortized Cost	22,035	15,880
Total short-term investments, Unrealized Gains	12	14
Total short-term investments, Unrealized Losses	(39)	(12)
Total short-term investments	22,008	15,882
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Total short-term investments, Amortized Cost	15,740	16,742
Total short-term investments, Unrealized Gains	44	50
Total short-term investments, Unrealized Losses	(12)	(3)
Total short-term investments	15,772	16,789
Cash
Schedule of Available-for-sale Securities [Line Items]
Total cash and cash equivalents, Amortized Cost	98,287	169,968
Total cash and cash equivalents, Unrealized Gains	0	0
Total cash and cash equivalents, Unrealized Losses	0	0
Total cash and cash equivalents, Estimated Fair Value	98,287	169,968
Money market mutual funds
Schedule of Available-for-sale Securities [Line Items]
Total cash and cash equivalents, Amortized Cost	635	164
Total cash and cash equivalents, Unrealized Gains	0	0
Total cash and cash equivalents, Unrealized Losses	0	0
Total cash and cash equivalents, Estimated Fair Value	635	164
Total cash and cash equivalents
Schedule of Available-for-sale Securities [Line Items]
Total cash and cash equivalents, Amortized Cost	98,922	170,132
Total cash and cash equivalents, Unrealized Gains	0	0
Total cash and cash equivalents, Unrealized Losses	0	0
Total cash and cash equivalents, Estimated Fair Value	$ 98,922	$ 170,132