Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended
	Oct. 26, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Equity [Line Items]
Authorized amount under share repurchase program	$ 50
Amendment Commencement date	Nov. 28, 2011
Amendment expiration date	Feb. 08, 2013
Term of plan, in years		10 years
Weighted average remaining contractual term option outstanding		2 years 8 months 12 days
Weighted average remaining contractual term option exercisable		1 year 8 months 12 days
Shares available for future grants		7,700,000	8,600,000	9,500,000
Total pre-tax intrinsic value of stock options exercised		6.7	5.0
Total pre-tax intrinsic value based on the closing stock price		$ 9.18
Intrinsic value of stock options outstanding		3.9
Intrinsic value of stock options exercisable		3.1
Common shares reserved for future issuance under the ESPP		4,000,000
Percentage of employee contribution from compensation		10.00%
Rate of discount from the fair market value		15.00%
Shares issued under the ESPP		3,300,000
Shares purchase by employees		300,000	400,000	400,000
Weighted-average price per share paid by the employees		$ 7.34	$ 4.35	$ 2.88
Weighted average remaining contractual term for unvested restricted shares, in years		1 year 9 months 18 days	2 years
Compensation cost expected to be recognized (in years)		2 years 6 months
Share-based payment awards in the form of stock option awards		470,000	511,000	746,000
Contractual term of stock options (in years)		7 years
Shares entitled to be purchased of a series of preferred stock under each right		One
Redemption of rights		$ 0.01
Percentage of common shares outstanding		15.00%
Minimum
Equity [Line Items]
Vesting period, in years		3 years
Maximum
Equity [Line Items]
Vesting period, in years		4 years
Unvested Stock Options
Equity [Line Items]
Total compensation cost not yet recognized		2.4
Restricted Stock
Equity [Line Items]
Total compensation cost not yet recognized		$ 8.9
Employee Stock Purchase Plan
Equity [Line Items]
Shares available for future grants		700,000
Shareholder Rights Plan
Equity [Line Items]
Exercise price under the shareholder rights plan		$ 50