Employee and Non-Employee Director Stock and Benefit Plans - Retirement Savings Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	$ 265,000
Maximum eligible compensation (as a percent)				4.00%
Company matching contribution, under the plan (as a percent)				50.00%
Benefit costs	4,900,000	$ 4,300,000	$ 4,600,000
Directors' Retainer Fee Subplan
Employee and Non Employee Director Benefit Plans
Benefit costs	1,200,000	$ 738,000	$ 714,000
Annual retainer fee received by non-employee directors, excluding the lead director and chairman, since 2006	60,000
Annual retainer fee received by lead director and chairman since August, 2008	$ 160,000
Deferred shares or units received	13,846	18,716	33,010
Deferred shares or units outstanding	199,225