Employee Savings, Stock Purchase and Supplemental Executive Retirement Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 hour M	Dec. 31, 2010	Dec. 31, 2009
Retirement Saving Opportunity Plan (RSOP)
Employee benefit plan
Eligibility requirement, initial period of employment for which part-time employees must complete 1,000 hours of service (in months)	12
Eligibility requirement, service hours that must be completed by part-time employees within the first 12 months of employment or within any plan year after the date of hire (in hours)	1,000
Total compensation expense related to Company's matching contributions	$ 1,800,000	$ 1,900,000	$ 3,600,000
Employee Stock Purchase Plan (ESPP)
Employee benefit plan
Employer contribution as a percentage of employee's payroll deduction	20.00%
Total compensation expense related to Company's matching contributions	153,000	135,000	160,000
Supplemental Executive Retirement plan
Employee benefit plan
Retirement plans vesting period (in years)	5
Cash surrender value of insurance contracts	11,100,000	10,100,000
Net periodic benefit (income) cost of plans	1,600,000	351,000	2,000,000
Service costs	347,000	204,000	2,500,000
Interest costs	731,000	660,000	1,800,000
Investment gain (loss)	(521,000)	513,000	2,300,000
Projected benefit obligations	$ 11,300,000	$ 10,300,000
Discount rate (as a percent)	7.00%	7.00%	7.90%