Shareholders' Equity Accumulated OCI Reclassified to Statement of Operations (Details) - USD ($) $ in Thousands		3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)												$ (59)	$ (138)	$ (70)
Other Amounts Recognized in Other Comprehensive Income, before tax												46	(68)	658
Income (loss) before income taxes		$ 23,202	$ (9,516)	$ 10,883	$ 6,387	$ 26,644	$ 147	$ 1,367	$ 26,791	$ 24,569	$ 33,178	37,102	(18,265)	(153,400)
Income Tax Expense (Benefit)		(9,932)	(4,098)	(5,030)	(2,557)	(5,223)	(1,061)	(9,128)	(6,284)	(19,060)	(8,841)	(22,099)	(4,035)	2,466
Net income (loss)		13,270	(13,614)	5,853	3,830	21,421	(914)	(7,761)	20,507	5,509	24,337	15,003	(22,300)	(150,934)
Total reclassifications for the period, net of tax		$ 13,270	$ (13,614)	$ 5,853	$ 3,830	$ 21,421	$ (914)	$ (7,761)	$ 20,507	$ 5,509	$ 24,337	15,003	(22,300)	(150,934)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	[1]											(1,726)	(755)	(1,379)
Total reclassifications for the period, net of tax	[1]											(1,726)	(755)	(1,379)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	[1],[2]											(59)	(138)	(70)
Defined Benefit Plan, Amortization of Gains (Losses)	[1],[2]											(1,979)	(572)	(926)
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements	[1],[2]											(375)	(55)	(325)
Other Amounts Recognized in Other Comprehensive Income, before tax	[1],[2]											(46)	0	(658)
Income (loss) before income taxes	[1]											(2,459)	(765)	(1,979)
Income Tax Expense (Benefit)	[1]											733	10	600
Net income (loss)	[1]											(1,726)	(755)	(1,379)
Total reclassifications for the period, net of tax	[1]											$ (1,726)	$ (755)	$ (1,379)

[1] Amounts in parenthesis indicate debits to the Consolidated Statements of Operations.

[2] These AOCI components are included in the computation of net periodic pension cost. Refer to Note 8 for additional details.