Shareholders' Equity - Amounts Reclassified from Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Amounts recognized as a component of net periodic pension and other postretirement benefit cost:
Total before income taxes	$ (5,105)	$ (6,309)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Amounts recognized as a component of net periodic pension and other postretirement benefit cost:
Total before income taxes	1,241	1,115
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Amounts recognized as a component of net periodic pension and other postretirement benefit cost:
Total before income taxes	(3,864)	(5,194)
Income tax benefit	1,349	1,808
Total reclassifications for the period, net of income taxes	$ (2,515)	$ (3,386)