Employee and Non-Employee Director Stock and Benefit Plans (Details 6) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Retirement Savings Plan (RSP)
Employee and Non Employee Director Benefit Plans
In accordance with the Internal Revenue Code, the maximum annual eligible compensation under the plan, prior to January 1, 2011	$ 250,000
Company guaranteed contribution, under the plan, prior to January 1, 2011 (as a percent)			3.00%
Company matching contribution, under the plan, prior to January 1, 2011 (as a percent)			66.667%
Maximum eligible compensation (as a percent)	4.00%	6.00%
Company matching contribution, under the plan (as a percent)	50.00%	50.00%
Benefit costs	5,500,000	6,600,000	10,200,000
Retirement Savings Plan (RSP) | Minimum
Employee and Non Employee Director Benefit Plans
Company discretionary contribution prior to January 1, 2011, based on profits (as a percent)			0.00%
Retirement Savings Plan (RSP) | Maximum
Employee and Non Employee Director Benefit Plans
Company discretionary contribution prior to January 1, 2011, based on profits (as a percent)			8.00%
Directors' Retainer Fee Subplan
Employee and Non Employee Director Benefit Plans
Benefit costs	854,000	769,000	647,000
Annual retainer fee received by lead director and chairman since August, 2008	160,000
Annual retainer fee received by non-employee directors, excluding the lead director and chairman, since 2006	$ 60,000
Deferred shares or units received	39,571	29,347	16,819
Deferred shares or units outstanding	105,421