Stock Plans (Tables)

12 Months Ended

Dec. 31, 2012

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]

Summary stock options activity is presented in the table below:

	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (thousands)
Balance at December 31, 2011 (1,789,061 shares exercisable)	4,994,581		$	15.11
Granted	596,930		$	22.79
Exercised	(693,015	)	$	10.25
Forfeited	(76,823	)	$	16.47
Expired	(10,857	)	$	19.22
Balance at December 31, 2012	4,810,816		$	16.73	7.1	$	33,266
Exercisable at December 31, 2012	1,937,245		$	14.30	5.6	$	18,213
Vested and expected to vest at December 31, 2012	4,173,444		$	16.26	7.0	$	30,821

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]

The following table provides the weighted-average fair value of the ESPP stock purchase rights during the years ended December 31, 2012, 2011 and 2010 and the assumptions used to calculate the fair value using the Black-Scholes-Merton option-pricing model:

	Year Ended December 31,
	2012			2011			2010
Volatility - weighted average	29.7		%	39.9		%	31.0		%
Volatility - range	22.6% to 35.2%			26.5% to 52.5%			21.2% to 45.9%
Risk-free interest rate - weighted average	0.07		%	0.06		%	0.15		%
Risk-free interest rate - range	0.02% to 0.10%			0.02% to 0.11%			0.08% to 0.17%
Dividend yield	—		%	—		%	—		%
Expected lives	3 months			3 months			3 months
Weighted-average fair value (per share)	$	3.63		$	3.70		$	3.56

Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]

Summary restricted stock activity is presented in the table below:

	Number of Shares		Weighted Average Grant Date Fair Value
Nonvested at December 31, 2011	1,185,500		$	18.82
Granted	299,030		$	21.99
Vested	(343,871	)	$	17.98
Forfeited	(34,530	)	$	18.40
Nonvested at December 31, 2012	1,106,129		$	19.73

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

The following table provides the fair value of options granted under the SCP during 2012, 2011 and 2010, together with a description of the assumptions used to calculate the fair value using the Black-Scholes-Merton option-pricing model:

	Year ended December 31,
	2012			2011			2010
Volatility	43.9		%	45.1		%	43.5		%
Risk-free interest rate - weighted average	0.8		%	1.0		%	2.5		%
Risk-free interest rate - range	0.81% to 1.03%			0.99% to 2.33%			2.50% to 2.75%
Dividend yield	—		%	—		%	—		%
Assumed forfeitures	8.0		%	8.0		%	8.0		%
Expected lives	5.7 years			5.4 years			5.5 years
Weighted-average fair value (per share)	$	9.46		$	6.85		$	7.42