Supplemental Equity Information - Reclassifications out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	$ 12,070	$ 2,422	$ 14,145	$ 4,322
Income tax effect	(896)	(942)	(1,693)	(1,680)
Total reclassifications, net of tax	11,174	1,480	12,452	2,642
Amortization of prior service cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	32	80	32	130
Amortization of actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	2,295	2,342	4,370	4,192
Reclassification of available for sale investment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	$ 9,743	$ 0	$ 9,743	$ 0