Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Shares
Options outstanding at December 31, 2012 (in shares)	201,000
Options granted (in shares)	0
Options exercised (in shares)	(9,000)	0
Options forfeited (in shares)	0
Options outstanding at March 31, 2013 (in shares)	192,000
Weighted Average Exercise Price
Options outstanding at December 31, 2012 (usd per share)	$ 3.60
Options granted (usd per share)	$ 0.00
Options exercised (usd per share)	$ 3.14
Options forfeited (usd per share)	$ 0.00
Options outstanding at March 31, 2013 (usd per share)	$ 3.62
Intrinsic value of options exercised	$ 87,000
Number Outstanding and Exercisable as of March 31, 2013
Intrinsic value of stock options outstanding	1,200,000
Weighted Average Grant Date Fair Value (per share)
Shares of restricted stock repurchased to satisfy tax withholding obligations	174,338	172,097
Aggregate intrinsic value of restricted shares	18,400,000
Total unrecognized compensation cost related to non-vested restricted shares	14,100,000
Compensation expense related to restricted shares	1,300,000	2,600,000
Employee Stock Purchase Program Valuation Assumptions
Expected term	6 months	6 months
Risk-free rate	0.11%	0.15%
Expected volatility	19.90%	29.40%
Dividend yield	0.00%	0.00%
Stock Options and Employee Stock Purchase Plan Rights
Weighted Average Grant Date Fair Value (per share)
Granted (usd per share)	$ 1.98	$ 1.93
Fair value of equity instrument other than options	29,000	46,000
Employee Stock Purchase Program Valuation Assumptions
Compensation expense related to options and ESPP rights	18,000	13,000
Cash received from exercise of options and ESPP	171,000	144,000
2009 Employee Stock Purchase Plan
Weighted Average Grant Date Fair Value (per share)
Total unrecognized compensation cost, weighted-average recognition period	4 months
Shares issued under the ESPP	20,170	19,823
ESPP purchase price (usd per share)	$ 7.11	$ 7.00
Employee Stock Purchase Program Valuation Assumptions
Intrinsic value of shares purchased ESPP	29,000
Intrinsic value of rights outstanding ESPP	30,000
Unrecognized compensation cost related to non-vested stock options	26,000
Restricted Stock
Restricted Stock
Unvested as of December 31, 2012 (in shares)	1,539,000
Granted (in shares)	1,180,000
Vested (shares)	(424,000)
Forfeited (shares)	(114,000)
Unvested as of March 31, 2013 (in shares)	2,181,000
Weighted Average Grant Date Fair Value (per share)
Unvested, Beginning Balance (usd per share)	$ 9.38
Granted (usd per share)	$ 9.25	$ 9.02
Vested (usd per share)	$ 8.98
Forfeited (usd per share)	$ 9.51
Unvested, Ending Balance (usd per share)	$ 9.38
Fair value of equity instrument other than options	$ 3,800,000	$ 4,200,000
Total unrecognized compensation cost, weighted-average recognition period	1 year 23 months 14 days
$1.37 to $4.10
Weighted Average Exercise Price
Lower Range of Exercise Price	$ 1.37
Upper Range of Exercise Price	$ 4.10
Number Outstanding and Exercisable as of March 31, 2013
Number outstanding (shares)	192,000
Weighted Average Remaining Contractual Life (in years)	11 months 1 day
Weighted Average Exercise Price (usd per share)	$ 3.62