Nature of Operations and Significant Accounting Policies (Details) Share Based Compensation (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
Number of issuable common shares for equity incentive plans	2,654,000
Deferred Compensation
Deferred compensation payable	$ 22,607,000	$ 36,315,000
Distribution of plan assets	16,800,000
Increase in fair value of plan assets	2,400,000
Deferred compensation expense	$ 2,400,000	$ 1,800,000	$ 7,500,000