Common Stock and Preferred Stock - Schedule of Mandatorily Redeemable Convertible Preferred Stock (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Series A Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Outstanding	557,339	557,339
Book Value	$ 15,605	$ 14,383
Series B Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Outstanding	515,836	515,836
Book Value	13,865	12,793
Series C Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Outstanding	3,551,060	3,551,060
Book Value	38,592	35,614
Series D Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Outstanding	2,430,054	2,430,054
Book Value	20,323	18,167
Series E Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Outstanding	1,063,951
Book Value	15,237
Mandatorily Redeemable [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Authorized	8,978,672
Shares Outstanding	8,118,240
Liquidation Preference	113,970
Book Value	103,622
Mandatorily Redeemable [Member] | Series A Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Authorized	564,083
Shares Outstanding	557,339
Liquidation Preference	15,628
Book Value	15,605
Mandatorily Redeemable [Member] | Series B Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Authorized	520,839
Shares Outstanding	515,836
Liquidation Preference	14,045
Book Value	13,865
Mandatorily Redeemable [Member] | Series C Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Authorized	3,659,375
Shares Outstanding	3,551,060
Liquidation Preference	38,709
Book Value	38,592
Mandatorily Redeemable [Member] | Series D Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Authorized	3,125,000
Shares Outstanding	2,430,054
Liquidation Preference	22,510
Book Value	20,323
Mandatorily Redeemable [Member] | Series E Preferred Stock [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Shares Authorized	1,109,375
Shares Outstanding	1,063,951
Liquidation Preference	23,078
Book Value	$ 15,237