Stock-Based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended											12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Stock Options	Dec. 31, 2012 Restricted Stock Units (RSUs) Installment	Dec. 31, 2011 Restricted Stock Units (RSUs)	Dec. 31, 2010 Restricted Stock Units (RSUs)	Dec. 31, 2012 Employee Stock Purchase Plan	Dec. 31, 2011 Employee Stock Purchase Plan	Dec. 31, 2010 Employee Stock Purchase Plan	Jun. 06, 2012 Employee Stock Purchase Plan	Dec. 31, 2012 Employee Stock Purchase Plan Maximum	Dec. 31, 2012 2008 Equity Incentive Plan	Jun. 06, 2012 2008 Equity Incentive Plan	Jun. 01, 2011 2008 Equity Incentive Plan	Dec. 31, 2012 2008 Equity Incentive Plan Stock Options	Dec. 31, 2012 2008 Equity Incentive Plan Performance-based Stock or Cash Awards	Dec. 31, 2011 2008 Equity Incentive Plan Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Purchase Plan, offering period												27 months
Employee Stock Purchase Plan, period for eligible employees to purchase												6 months
Employee Stock Purchase Plan, purchase price of common stock as percentage of fair market value								85.00%					100.00%
Employee Stock Purchase Plan, authorized shares for issuance									820,500								500,000
Increase in shares of common stock authorized for issuance											500,000			3,000,000	2,000,000
Maximum number of shares of common stock authorized for issuance											1,320,500			13,540,940
Number of shares available for future issuance								581,879					4,300,000
Stock-based compensation, award term													10 years
Stock-based compensation, vesting period					3 years											4 years
Stock option plan granted on cash award																	$ 1.0
Performance-based stock options, outstanding													50,000
Stock-based compensation, shares granted																		50,000
Aggregate number of shares of common stock reserved for future issuance	12,900,000
Outstanding options and other stock based awards	8,600,000
Total intrinsic value of options exercised	0.3	0.2	0.3
Stock-based compensation, number of installments from grant date to vest					3
Fair value of restricted stock units which vested during the year					0.04	0.10	0.05
Stock-based compensation expense expected to be recognized				$ 4.3
Stock-based compensation, weighted average recognition period				2 years 5 months 19 days
Stock-based compensation, expected dividend yield	0.00%
Weighted average grant-date fair value of stock options granted	$ 2.13	$ 1.37	$ 1.94
Weighted average grant-date fair value of awards granted					$ 3.03		$ 1.85	$ 1.43	$ 0.68	$ 0.90