Convertible Preferred Stock - Redemption Requirement of Common Stock (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Class of Stock [Line Items]
Redemption requirements	$ 19,313
2012
Class of Stock [Line Items]
Redemption requirements	0
2013
Class of Stock [Line Items]
Redemption requirements	0
2014
Class of Stock [Line Items]
Redemption requirements	2,626
2015
Class of Stock [Line Items]
Redemption requirements	8,567
2016
Class of Stock [Line Items]
Redemption requirements	8,120
Series A redeemable convertible preferred stock [Member]
Class of Stock [Line Items]
Redemption requirements	4,586
Series A redeemable convertible preferred stock [Member] | 2012
Class of Stock [Line Items]
Redemption requirements	0
Series A redeemable convertible preferred stock [Member] | 2013
Class of Stock [Line Items]
Redemption requirements	0
Series A redeemable convertible preferred stock [Member] | 2014
Class of Stock [Line Items]
Redemption requirements	216
Series A redeemable convertible preferred stock [Member] | 2015
Class of Stock [Line Items]
Redemption requirements	2,263
Series A redeemable convertible preferred stock [Member] | 2016
Class of Stock [Line Items]
Redemption requirements	2,107
Series B redeemable convertible preferred stock [Member]
Class of Stock [Line Items]
Redemption requirements	8,727
Series B redeemable convertible preferred stock [Member] | 2012
Class of Stock [Line Items]
Redemption requirements	0
Series B redeemable convertible preferred stock [Member] | 2013
Class of Stock [Line Items]
Redemption requirements	0
Series B redeemable convertible preferred stock [Member] | 2014
Class of Stock [Line Items]
Redemption requirements	410
Series B redeemable convertible preferred stock [Member] | 2015
Class of Stock [Line Items]
Redemption requirements	4,304
Series B redeemable convertible preferred stock [Member] | 2016
Class of Stock [Line Items]
Redemption requirements	4,013
Series C redeemable convertible preferred stock [Member]
Class of Stock [Line Items]
Redemption requirements	6,000
Series C redeemable convertible preferred stock [Member] | 2012
Class of Stock [Line Items]
Redemption requirements	0
Series C redeemable convertible preferred stock [Member] | 2013
Class of Stock [Line Items]
Redemption requirements	0
Series C redeemable convertible preferred stock [Member] | 2014
Class of Stock [Line Items]
Redemption requirements	2,000
Series C redeemable convertible preferred stock [Member] | 2015
Class of Stock [Line Items]
Redemption requirements	2,000
Series C redeemable convertible preferred stock [Member] | 2016
Class of Stock [Line Items]
Redemption requirements	$ 2,000