Convertible Preferred Stock Balances (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Preferred Stock [Line Items]
Shares Authorized	60,152,555	39,108,536
Shares Issued and Outstanding	12,329,330	10,657,030
Carrying Value	$ 102,023	$ 83,178
Liquidation Amount	105,512	85,262
Series A Preferred Stock
Preferred Stock [Line Items]
Shares Authorized	1,527,611	1,527,611
Shares Issued and Outstanding	428,922	428,922
Carrying Value	1,835	1,835
Liquidation Amount	2,200	2,200
Series B-1 Preferred Stock
Preferred Stock [Line Items]
Shares Authorized	3,425,152	3,425,152
Shares Issued and Outstanding	961,720	961,720
Carrying Value	4,726	4,726
Liquidation Amount	4,932	4,932
Series B-2 Preferred Stock
Preferred Stock [Line Items]
Shares Authorized	14,811,323	14,811,323
Shares Issued and Outstanding	4,119,759	4,119,759
Carrying Value	21,039	21,039
Liquidation Amount	21,128	21,128
Series C Preferred Stock
Preferred Stock [Line Items]
Shares Authorized	6,944,450	6,944,450
Shares Issued and Outstanding	1,949,874	1,949,874
Carrying Value	19,905	19,905
Liquidation Amount	20,000	20,000
Series D Preferred Stock
Preferred Stock [Line Items]
Shares Authorized	11,385,196	12,400,000
Shares Issued and Outstanding	3,196,755	3,196,755
Carrying Value	35,673	35,673
Liquidation Amount	37,002	37,002
Series E Preferred Stock
Preferred Stock [Line Items]
Shares Authorized	22,058,823
Shares Issued and Outstanding	1,672,300
Carrying Value	18,845
Liquidation Amount	$ 20,250