Shareholders' Equity - Amounts Reclassified from Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net reclassification adjustments for amounts recognized in net income as a component of net periodic benefit cost, tax expense	$ 1,854	$ 1,313	$ 5,502	$ 3,899
Total reclassifications for the period, net of income taxes	(3,456)	(2,453)	(10,255)	(7,281)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of net loss	(6,450)	(4,909)	(19,138)	(14,570)
Amortization of prior service credit	1,140	1,142	3,381	3,390
Total before income taxes	(5,310)	(3,767)	(15,757)	(11,180)
Net reclassification adjustments for amounts recognized in net income as a component of net periodic benefit cost, tax expense	1,854	1,314	5,502	3,899
Total reclassifications for the period, net of income taxes	$ (3,456)	$ (2,453)	$ (10,255)	$ (7,281)