Equity-based Incentive Plans (Details 4) (USD $) Share data in Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other Share-based Compensation Disclosures
Total expenses for the plan	$ 12,500,000	$ 17,300,000	$ 14,700,000
Stock options
Equity Based Compensation
Aggregate intrinsic value of options exercised (in dollars)	3,100,000	7,400,000	11,600,000
Aggregate intrinsic value of options that are currently outstanding and that are expected to be exercised (in dollars)	11,700,000
Fair value assumptions
Volatility minimum (as a percent)		65.10%	66.40%
Volatility maximum (as a percent)		66.30%	67.00%
Risk-free interest rate minimum (as a percent)		0.40%	0.80%
Risk-free interest rate maximum (as a percent)		1.40%	2.00%
Stock options | Minimum
Fair value assumptions
Dividend yield (as a percent)		2.30%	2.00%
Expected life		2 years 9 months 18 days	2 years 9 months 18 days
Stock options | Maximum
Fair value assumptions
Dividend yield (as a percent)		2.50%	2.20%
Expected life		4 years 1 month 6 days	4 years 1 month 6 days
2008 Executive Incentive Compensation Plan (Executive Plan) | Stock options
Other Share-based Compensation Disclosures
Market value of award	135,000	4,000,000	208,000
Fair value assumptions
Vesting period	3 years
Original number of shares authorized for issuance	2.5
Remaining number of shares available for issuance	1.9
2004 Employee Stock Purchase Plan
Other Share-based Compensation Disclosures
Maximum annual allowable payroll deduction per employee	10,400
Employer's matching contribution of employees' payroll deductions (as a percent)	10.00%
Total expenses for the plan	$ 354,000	$ 328,000	$ 299,000