Non-Qualified Retirement, Savings and Investment Plans (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2009	Dec. 31, 2012
Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Number of non-qualified retirement savings and investment plans	2		2
Investments, employee benefit plans, at fair value	$ 14,950,000		$ 14,950,000			$ 12,755,000
Executive Deferred Compensation Plan [Member]
Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Basis points					300
Deferred compensation liability, current and long-term	10,900,000		10,900,000			11,700,000
Compensation expense	300,000	200,000	700,000	700,000
Assets held-in-trust	3,800,000		3,800,000			6,000,000
Assets held-in-trust, current	400,000		400,000
Investment gains (losses)	200,000	100,000	300,000	1,200,000
Common stock held by plan	200,000		200,000			100,000
Non-Qualified Plan [Member]
Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Deferred compensation liability, current and long-term	12,800,000		12,800,000			11,200,000
Investment gains (losses)	500,000	400,000	1,100,000	1,000,000
Common stock held by plan	1,200,000		1,200,000			1,000,000
Increase (decrease) in compensation expense	600,000	200,000	1,300,000	800,000
Investments, employee benefit plans, at fair value	$ 11,600,000		$ 11,600,000			$ 10,200,000