Postretirement Medical Benefits (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Number of former union employees not covered under plan	41
Accumulated other comprehensive (income) loss (pre-tax) related to [Abstract]
Estimated net loss expected to be amortized from accumulated other comprehensive income	$ 1,700,000
Prior service cost (credit) expected to be amortized from accumulated other comprehensive income	(100,000)
One-percentage-point change in assumed health care cost trend rates [Abstract]
Effect on total of service and interest cost components, 1-Percentage-Point Increase	1,000
Effect on total of service and interest cost components, 1-Percentage-Point Decrease	(1,000)
Effect on postretirement benefit obligation, 1-Percentage-Point Increase	33,000
Effect on postretirement benefit obligation, 1-Percentage-Point Decrease	(34,000)
Postretirement Benefits [Member]
Net Periodic benefit costs related to retirement plans [Abstract]
Net periodic benefit cost	(939,000)	(1,874,000)	(1,969,000)
Summary of expected future benefit payments [Abstract]
2015	2,257,000
2016	1,300,000
2017	68,000
2018	64,000
2019	60,000
Years 2020 - 2024	226,000
Supplemental Executive Retirement Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	5,661,000	4,725,000
Service cost	164,000	180,000	130,000
Interest cost	277,000	235,000	186,000
Actuarial loss (gain)	436,000	521,000
Benefit obligation at end of year	6,538,000	5,661,000	4,725,000
(Unfunded) status of the plans	(6,538,000)	(5,661,000)
Amounts recognized in the balance sheet [Abstract]
Accrued postretirement benefit liabilities	6,538,000	5,661,000
Accumulated other comprehensive (income) loss (pre-tax) related to [Abstract]
Unrecognized net actuarial losses (gains)	1,389,000	1,342,000
Unrecognized prior service cost (credit)	0	0
Net Periodic benefit costs related to retirement plans [Abstract]
Service cost	164,000	180,000	130,000
Interest cost	277,000	235,000	186,000
Amortization of prior service cost	0	28,000	110,000
Amortization of net actuarial loss	388,000	690,000	261,000
Net periodic benefit cost	829,000	1,133,000	687,000
Actuarial assumptions used to determine costs and benefit obligations related to postretirement plan [Abstract]
Discount rate (in hundredths)	4.00%	4.90%	4.00%
Summary of expected future benefit payments [Abstract]
2015	7,143,000
2016	0
2017	0
2018	0
2019	0
Years 2020 - 2024	0
U.S. Postretirement Benefit Plans [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	4,960,000	5,950,000
Service cost	1,000	1,000	4,000
Interest cost	26,000	33,000	81,000
Benefits paid	(772,000)	(850,000)
Actuarial loss (gain)	(23,000)	(174,000)
Translation adjustment	0	0
Benefit obligation at end of year	4,192,000	4,960,000	5,950,000
(Unfunded) status of the plans	(4,192,000)	(4,960,000)
Amounts recognized in the balance sheet [Abstract]
Accrued postretirement benefit liabilities	4,192,000	4,960,000
Accumulated other comprehensive (income) loss (pre-tax) related to [Abstract]
Unrecognized net actuarial losses (gains)	2,973,000	5,087,000
Unrecognized prior service cost (credit)	0	(2,888,000)
Net Periodic benefit costs related to retirement plans [Abstract]
Service cost	1,000	1,000	4,000
Interest cost	26,000	33,000	81,000
Amortization of prior service cost	(2,888,000)	(4,206,000)	(4,752,000)
Amortization of unrecognized loss	2,092,000	2,548,000	2,887,000
Net periodic benefit cost	(769,000)	(1,624,000)	(1,780,000)
Actuarial assumptions used to determine costs and benefit obligations related to postretirement plan [Abstract]
Discount rate (in hundredths)	0.55%	0.45%	0.55%
Canadian Postretirement Benefit Plans [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	126,000	156,000
Service cost	0	0	0
Interest cost	4,000	5,000	5,000
Benefits paid	(26,000)	(21,000)
Actuarial loss (gain)	17,000	(4,000)
Translation adjustment	(11,000)	(10,000)
Benefit obligation at end of year	110,000	126,000	156,000
(Unfunded) status of the plans	(110,000)	(126,000)
Amounts recognized in the balance sheet [Abstract]
Accrued postretirement benefit liabilities	110,000	126,000
Accumulated other comprehensive (income) loss (pre-tax) related to [Abstract]
Unrecognized net actuarial losses (gains)	(65,000)	(129,000)
Unrecognized prior service cost (credit)	(201,000)	(335,000)
Net Periodic benefit costs related to retirement plans [Abstract]
Service cost	0	0	0
Interest cost	4,000	5,000	5,000
Amortization of prior service cost	(129,000)	(140,000)	(142,000)
Amortization of net actuarial loss	(45,000)	(115,000)	(52,000)
Net periodic benefit cost	$ (170,000)	$ (250,000)	$ (189,000)
Actuarial assumptions used to determine costs and benefit obligations related to postretirement plan [Abstract]
Discount rate (in hundredths)	3.00%	3.50%	3.00%
Current medical cost trend rate (in hundredths)	6.43%	7.14%	8.57%
Ultimate medical cost trend rate (in hundredths)	5.00%	5.00%	5.00%
Year trend rate declines to ultimate	2017	2017	2017