Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive loss, beginning balance				$ (18,712)					$ (18,712)
Amounts reclassified from accumulated other comprehensive income (loss)									32,217		(49,879)	19,772
Accumulated other comprehensive income (loss), ending balance	(49,638)				(18,712)				(49,638)		(18,712)
Amortization of Pension and Postretirement Plan items
Tax (expense) benefit	1,560	410	1,461	(904)	12,622	495	(1,464)	(1,409)	2,527		10,244	1,657
NET LOSS	(5,128)	1,099	5,295	(3,573)	1,611	(18,615)	(5,362)	(15,947)	(2,307)		(38,313)	(178,007)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Amortization of Pension and Postretirement Plan items
Prior service costs									(10)	[1]	583
Actuarial gain									32,737	[1]	46,575
Amortization of net actuarial gain									(510)	[1]	2,721
Total before tax									32,217		49,879
Tax (expense) benefit									(1,291)		(16,757)
NET LOSS									30,926		33,122
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Plan [Member]
Amortization of Pension and Postretirement Plan items
Prior service costs									(44)		44
Actuarial gain									20,674		35,568
Amortization of net actuarial gain									(211)		2,607
Total before tax									20,419		38,219
Tax (expense) benefit									(688)		(12,481)
NET LOSS									19,731		25,738
Reclassification out of Accumulated Other Comprehensive Income [Member] | Post Retirement Plan [Member]
Amortization of Pension and Postretirement Plan items
Prior service costs									34		539
Actuarial gain									12,063		11,007
Amortization of net actuarial gain									(299)		114
Total before tax									11,798		11,660
Tax (expense) benefit									(603)		(4,276)
NET LOSS									11,195		7,384
Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income (loss), ending balance	(49,638)				(18,712)				(49,638)		(18,712)	(51,834)
Accumulated Defined Benefit Plans Adjustment [Member] | Pension Plan [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income (loss), ending balance	(40,160)				(20,429)				(40,160)		(20,429)	(46,167)
Accumulated Defined Benefit Plans Adjustment [Member] | Post Retirement Plan [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income (loss), ending balance	(9,478)				1,717				(9,478)		1,717	(5,667)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)									(30,926)		33,122
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Plan [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)									(19,731)		25,738
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Post Retirement Plan [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)									$ (11,195)		$ 7,384

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension