Equity - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 08, 2014	Dec. 12, 2012
Equity [Line Items]
Payments for Repurchase of Common Stock	$ 0	$ 15,494,000	$ 427,000
Shares absorbed into plan	5,700,000
Term of plan, in years	10 years
Weighted average remaining contractual term option outstanding	4 years 7 months
Weighted average remaining contractual term option exercisable	3 years 1 month
Shares available for future grants	11,600,000	6,800,000	7,700,000
Total pre-tax intrinsic value of stock options exercised	3,300,000	1,800,000
Total pre-tax intrinsic value based on the closing stock price	$ 13.21
Intrinsic value of stock options outstanding	7,200,000
Intrinsic value of stock options exercisable	3,900,000
Percentage of employee contribution from compensation	10.00%
Weighted average remaining contractual term for unvested restricted shares, in years	2 years 4 months	2 years
Compensation cost expected to be recognized (in years)	2 years 7 months
Share-based payment awards in the form of stock option awards	651,000	553,000	470,000
Contractual term of stock options (in years)	7 years
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	3,700,000
Restricted Stock
Equity [Line Items]
Total compensation cost not yet recognized		11,800,000
BOD authorized plan
Equity [Line Items]
Authorized amount under share repurchase program					$ 50,000,000
Share repurchase plan commencement date					Dec. 12, 2012
Share repurchase plan expiration date				Feb. 07, 2014
Employee Stock Purchase Plan
Equity [Line Items]
Shares available for future grants	200,000
Common shares reserved for future issuance under the ESPP	4,000,000
Rate of discount from the fair market value	15.00%
Shares issued under the ESPP	3,800,000
Shares purchase by employees	200,000	200,000	300,000
Weighted-average price per share paid by the employees	$ 10.57	$ 8.00	$ 7.34
Shareholder Rights Plan
Equity [Line Items]
Shares entitled to be purchased of a series of preferred stock under each right	one-hundredth
Exercise price under the shareholder rights plan	$ 50
Redemption of rights	$ 0.01
Percentage of common shares outstanding	15.00%