Summary by Exercise Price of Outstanding Options, Vested Options, Options Vested and Expected to Vest (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Stock Options Outstanding	10,828,682	10,255,222
Weighted Average Remaining Contractual Life of Outstanding Stock Options (years)	8 years 26 days
Number of Stock Options Vested and Expected to Vest	10,362,887
$0.01 - $1.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Limit	$ 0.01
Exercise Price Range, Upper Limit	$ 1.00
Stock Options Outstanding	4,994,901
Weighted Average Remaining Contractual Life of Outstanding Stock Options (years)	6 years 10 months 17 days
Number of Stock Options Vested	3,072,543
Number of Stock Options Vested and Expected to Vest	4,921,642
$1.01 - $5.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Limit	$ 1.01
Exercise Price Range, Upper Limit	$ 5.00
Stock Options Outstanding	3,076,531
Weighted Average Remaining Contractual Life of Outstanding Stock Options (years)	8 years 7 months 2 days
Number of Stock Options Vested	776,508
Number of Stock Options Vested and Expected to Vest	2,915,612
$5.01 - $10.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Limit	$ 5.01
Exercise Price Range, Upper Limit	$ 10.00
Stock Options Outstanding	1,150,750
Weighted Average Remaining Contractual Life of Outstanding Stock Options (years)	9 years 4 months 13 days
Number of Stock Options Vested	25,059
Number of Stock Options Vested and Expected to Vest	1,067,147
$10.01 - $20.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Limit	$ 10.01
Exercise Price Range, Upper Limit	$ 20.00
Stock Options Outstanding	1,606,500
Weighted Average Remaining Contractual Life of Outstanding Stock Options (years)	9 years 10 months 6 days
Number of Stock Options Vested	1,624
Number of Stock Options Vested and Expected to Vest	1,458,486
$0.01 - $20.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Limit	$ 0.01
Exercise Price Range, Upper Limit	$ 20.00
Stock Options Outstanding	10,828,682
Weighted Average Remaining Contractual Life of Outstanding Stock Options (years)	8 years 26 days
Number of Stock Options Vested	3,875,734
Number of Stock Options Vested and Expected to Vest	10,362,887