Stock-Based Compensation - Narrative (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	1 Months Ended	3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Equity Incentive Plan 2008	Jun. 30, 2013 Equity Incentive Plan 2008	Jan. 31, 2013 Equity Incentive Plan 2008 Stock Option	Jun. 30, 2013 Equity Incentive Plan 2008 Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares to be issued for cancellation or repurchase of options under the 1998 plan						3,084,848
Shares issued for cancellation or repurchase of options under the 1998 plan						365,696
Annual increase provision, allowable percentage						5.00%
Annual increase provision, maximum allowable shares						1,785,714
Increase in authorized shares							1,294,874
Stock options, number of shares reserved for issuance					5,835,258	5,835,258
Stock options, maximum term	5 years 6 months	5 years 6 months	5 years 6 months	5 years 8 months 15 days				10 years
Stock options, average vesting period					4 years
Unvested options outstanding	1,768,033		1,768,033
Unvested options outstanding, vesting period			2 years 4 months 24 days
Unrecognized compensation expense	$ 8.0		$ 8.0