Non-Qualified Retirement, Savings and Investment Plans (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) plan shares	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) plan shares	Sep. 30, 2014 USD ($)	Dec. 31, 2009	Dec. 31, 2014 USD ($)
Non-Qualified Retirement, Savings and Investment Plans [Line Items]
Number of non-qualified retirement savings and investment plans | plan	2		2
Assets held in trust, current	$ 174		$ 174			$ 214
Executive Deferred Compensation Plan [Member]
Non-Qualified Retirement, Savings and Investment Plans [Line Items]
Investment yield, basis spread on variable rate					3.00%
Deferred compensation liability, current and long-term	10,300		10,300			10,200
Compensation expense	(200)	$ 48	100	$ 400
Diversified investments held in trust	5,300		5,300			4,600
Assets held in trust, current	200		200
Investment gains (losses)	$ (300)	(100)	$ (300)	41
Shares of Common Stock held by plan | shares	0		0
Common stock held by plan						200
Non-Qualified Plan [Member]
Non-Qualified Retirement, Savings and Investment Plans [Line Items]
Deferred compensation liability, current and long-term	$ 12,000		$ 12,000			14,400
Diversified investments held in trust	12,000		12,000			13,100
Investment gains (losses)	(800)	(300)	(800)	100
Common stock held by plan						$ 1,300
Increase (decrease) in compensation expense	$ (800)	$ (100)	$ (1,100)	$ 100