Stock- Based Compensation - Details of stock option activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2007
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding, Beginning Balance	1,737,881
Number of Shares, Granted	589,934		244,043	545,930	283,254
Number of Shares, Exercised	(798,967)
Number of Shares, Expired	(32,800)
Number of Shares, Cancelled	(9,697)
Outstanding, Ending Balance	1,486,351	1,737,881
Exercisable, Ending Balance	600,144
Available For Grant	2,516,117
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 13.95
Weighted Average Exercise Price, Granted	$ 15.63
Weighted Average Exercise Price, Exercised	$ 20.97
Weighted Average Exercise Price, Expired	$ 17.16
Weighted Average Exercise Price, Cancelled	$ 21.93
Weighted Average Exercise Price, Outstanding, Ending Balance	$ 17.63	$ 13.95
Weighted average exercise price, exercisable	$ 17.54
Aggregate Intrinsic Value, Outstanding	$ 11,503
Aggregate Intrinsic Value, Exercisable	4,693
Weighted average grant-date fair value of option granted	$ 7.33	$ 11.57	$ 9.01
Aggregate intrinsic value of options exercised	10,256	3,515	5,279
Total fair value of shares vested	$ 2,641	$ 1,655	$ 899