Pension and Other Post-retirement Benefit Plans (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension Benefits
Components of net periodic benefit cost recognized
Service cost	$ 380,000	$ 576,000	$ 1,138,000	$ 1,866,000
Interest cost	2,452,000	2,653,000	7,360,000	8,163,000
Expected return on plan assets	(3,247,000)	(3,566,000)	(9,710,000)	(10,895,000)
Amortization of:
Prior service (benefit) cost	80,000	273,000	625,000	822,000
Actuarial loss	1,233,000	1,380,000	3,666,000	3,933,000
Settlements	801,000	12,077,000	2,121,000	14,317,000
Curtailment			5,369,000
Special termination benefit impact			4,721,000
Net periodic benefit cost	1,699,000	13,393,000	15,290,000	18,206,000
Anticipated contributions	600,000		600,000
Pension Benefits | Sale of specialty paper business
Amortization of:
Settlements		7,700,000		7,700,000
Pension Benefits | Previously disclosed
Amortization of:
Anticipated contributions	800,000		800,000
Other Post-retirement Benefits
Components of net periodic benefit cost recognized
Service cost	76,000	508,000	1,191,000	1,524,000
Interest cost	488,000	1,039,000	2,129,000	3,117,000
Amortization of:
Prior service (benefit) cost	(190,000)	(770,000)	(1,715,000)	(2,310,000)
Actuarial loss	67,000	788,000	1,251,000	2,364,000
Curtailment			(16,004,000)	(634,000)
Net periodic benefit cost	441,000	1,565,000	(13,148,000)	4,061,000
Contributions by employer			2,700,000
Other Post-retirement Benefits | Previously disclosed
Amortization of:
Anticipated contributions	4,700,000		4,700,000
Other Post-retirement Benefits | Plan Expectation
Amortization of:
Contributions by employer			$ 3,600,000