Supplemental Equity Information - 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
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ 2,553,005	$ 2,456,744
Amounts reclassified from AOCL	$ 11,174	$ 1,480	12,452	2,642
Other comprehensive income (loss), net of tax	12,599	(7,974)	13,847	(7,594)
Ending Balance	874,178	2,434,186	874,178	2,434,186
Retirement Plans
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(126,063)	(115,334)	(127,341)	(116,496)
Other comprehensive loss before reclassifications	0	0	0	0
Amounts reclassified from AOCL	1,431	1,480	2,709	2,642
Other comprehensive income (loss), net of tax	1,431	1,480	2,709	2,642
Ending Balance	(124,632)	(113,854)	(124,632)	(113,854)
Foreign Currency Translation
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(27,363)	(19,494)	(28,560)	(20,129)
Other comprehensive loss before reclassifications	3,755	(3,788)	4,952	(3,153)
Amounts reclassified from AOCL	0	0	0	0
Other comprehensive income (loss), net of tax	3,755	(3,788)	4,952	(3,153)
Ending Balance	(23,608)	(23,282)	(23,608)	(23,282)
Other
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(7,965)	3,691	(5,672)	5,674
Other comprehensive loss before reclassifications	586	(2,292)	(1,707)	(4,275)
Amounts reclassified from AOCL	9,743	0	9,743	0
Other comprehensive income (loss), net of tax	10,329	(2,292)	8,036	(4,275)
Ending Balance	2,364	1,399	2,364	1,399
Total
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(161,391)	(131,137)	(161,573)	(130,951)
Other comprehensive loss before reclassifications	4,341	(6,080)	3,245	(7,428)
Amounts reclassified from AOCL	11,174	1,480	12,452	2,642
Other comprehensive income (loss), net of tax	15,515	(4,600)	15,697	(4,786)
Ending Balance	$ (145,876)	$ (135,737)	$ (145,876)	$ (135,737)