Stock Option Activity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Arrangements with Employees and Nonemployees [Abstract]
Shares outstanding at beginning of year	3,331,031	5,007,337	7,755,254
Shares granted	208,400	468,000	342,250
Shares exercised	(613,691)	(1,738,741)	(2,133,806)
Shares forfeited or expired	(304,054)	(405,565)	(956,361)
Shares outstanding at end of year	2,621,686	3,331,031	5,007,337	7,755,254
Shares exercisable at December 31, 2012	1,992,151
Shares vested and expected to vest at December 31, 2012	2,485,086
Weighted average exercise price of options outstanding at beginning of year	$ 11.91	$ 9.10	$ 7.67
Weighted average exercise price of options granted	$ 16.84	$ 19.81	$ 12.68
Weighted average exercise price of options exercised	$ 6.04	$ 6.28	$ 3.37
Weighted average exercise price of options forfeited or expired	$ 17.55	$ 10.46	$ 11.56
Weighted average exercise price of options outstanding at end of year	$ 13.03	$ 11.91	$ 9.10	$ 7.67
Weighted average exercise price of options exercisable at December 31, 2012	$ 12.36
Weighted average exercise price of options vested and expected to vest at December 31, 2012	$ 12.78
Weighted average remaining contractual life (years) outstanding	5 years 6 months	6 years 4 months	6 years 4 months	7 years 6 months
Weighted average remaining contractual life (years) exercisable at December 31, 2012	4 years 9 months
Weighted average remaining contractual life (years) vested and expected to vest at December 31, 2012	5 years 4 months
Aggregate intrinsic value outstanding	$ 11,373	$ 18,468	$ 47,009	$ 15,920
Aggregate intrinsic value exercisable at December 31, 2012	10,000
Aggregate intrinsic value vested and expected to vest at December 31, 2012	$ 11,330