Retirement Benefits - Postretirement Benefit Health Care Cost Trend Rates and Net Periodic Benefit Cost (Details 8) - Postretirement Benefit - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Health care cost trend rates
Health care cost trend rates in next fiscal year (as a percent)	7.25%
Health care cost trend rates in 2025 and beyond (as a percent)	5.00%
A one-percentage-point change in assumed health care cost trend rates
Effect of a one percent annual increase in the assumed cost trend rates on the accumulated postretirement benefit obligation	$ 300
Effect of a one percent annual decrease in the assumed cost trend rates on the accumulated postretirement benefit obligation	200
Net periodic benefit cost
Interest cost	335	$ 388	$ 351
Recognized net actuarial loss	40	151	341
Net periodic pension expense	375	539	692
Change in accumulated benefit obligation
Benefit obligation at beginning of year	11,310	12,629
Interest cost	335	388	351
Employee contributions	543	356
Actuarial (gain) loss	(1,722)	(252)
Benefits paid	(1,735)	(1,811)
Benefit obligation at end of year	8,731	11,310	$ 12,629
Funded status - (Under)/overfunded	(8,731)	(11,310)
Amounts recognized in the Consolidated Balance Sheet
Unrecognized net actuarial gains (losses) classified in accumulated other comprehensive loss	1,000	(1,000)
Accumulated postretirement benefit obligation classified in current liabilities	$ 2,000	$ 2,000
Assumptions used for determining accumulated benefit obligation
Discount rate (as a percent)	3.45%	3.25%
Maximum
A one-percentage-point change in assumed health care cost trend rates
Effect of a one percent annual increase in the assumed cost trend rates on the accumulated postretirement benefit obligation interest cost	$ 100
Effect of a one percent annual decrease in the assumed cost trend rates on the accumulated postretirement benefit obligation interest cost	$ 100