Retirement Plans and Other Benefits - Amounts Recognized on the Consolidated Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Amounts recognized on the Consolidated Balance Sheets
Assets for other postretirement benefits	$ 152,290	$ 0
Noncurrent liability	(453,736)	(513,628)
Pension Benefits
Amounts recognized on the Consolidated Balance Sheets
Assets for other postretirement benefits	0	0
Current liability	(9,508)	(10,860)
Noncurrent liability	(453,736)	(371,549)
Net amount recognized	(463,244)	(382,409)
Other Benefits
Amounts recognized on the Consolidated Balance Sheets
Assets for other postretirement benefits	152,290	0
Current liability	0	0
Noncurrent liability	0	(142,079)
Net amount recognized	$ 152,290	$ (142,079)