Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenue	$ 1,049,117	$ 842,820	$ 821,371	$ 836,640	$ 887,069	$ 839,031	$ 835,886	$ 844,589	$ 3,549,948	$ 3,406,575	$ 3,578,060
Interest expense									(113,497)	(88,970)	(87,583)
Tax (benefit) provision	(32,326)	$ 17,607	$ 4,952	31,416	38,204	23,197	33,394	37,024	21,649	131,819	189,778
Net income					(79,079)	$ 70,105	$ 58,184	62,640	261,340	111,850	426,318
Accumulated Other Comprehensive Income (Loss)
Balance at				(940,133)				(888,635)	(940,133)	(888,635)	(846,156)
Other comprehensive income (loss) before reclassifications									119,446	(77,619)	(73,459)
Amounts reclassified from accumulated other comprehensive income (loss)									28,514	26,121	30,980
Other comprehensive income (loss)									147,960	(51,498)	(42,479)
Balance at	(792,173)				(940,133)				(792,173)	(940,133)	(888,635)
Cash flow hedges
Accumulated Other Comprehensive Income (Loss)
Balance at				(1,485)				(3,912)	(1,485)	(3,912)	(4,689)
Other comprehensive income (loss) before reclassifications									(288)	1,095	546
Amounts reclassified from accumulated other comprehensive income (loss)									1,367	1,332	231
Other comprehensive income (loss)									1,079	2,427	777
Balance at	(406)				(1,485)				(406)	(1,485)	(3,912)
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
Balance at				120				536	120	536	2,966
Other comprehensive income (loss) before reclassifications									1,158	(1,109)	(1,715)
Amounts reclassified from accumulated other comprehensive income (loss)									319	693	(715)
Other comprehensive income (loss)									1,477	(416)	(2,430)
Balance at	1,597				120				1,597	120	536
Pension and postretirement benefit plans
Accumulated Other Comprehensive Income (Loss)
Balance at				(787,813)				(738,768)	(787,813)	(738,768)	(786,079)
Other comprehensive income (loss) before reclassifications									12,185	(73,141)	19,146
Amounts reclassified from accumulated other comprehensive income (loss)									26,828	24,096	28,165
Other comprehensive income (loss)									39,013	(49,045)	47,311
Balance at	(748,800)				(787,813)				(748,800)	(787,813)	(738,768)
Foreign currency adjustments
Accumulated Other Comprehensive Income (Loss)
Balance at				$ (150,955)				$ (146,491)	(150,955)	(146,491)	(58,354)
Other comprehensive income (loss) before reclassifications									106,391	(4,464)	(91,436)
Amounts reclassified from accumulated other comprehensive income (loss)									0	0	3,299
Other comprehensive income (loss)									106,391	(4,464)	(88,137)
Balance at	$ (44,564)				$ (150,955)				(44,564)	(150,955)	(146,491)
Amounts Reclassified from AOCI | Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenue									(179)	68	1,082
Cost of sales									(32)	(222)	551
Interest expense									(2,028)	(2,028)	(2,028)
Total before tax									(2,239)	(2,182)	(395)
Tax (benefit) provision									(872)	(850)	(164)
Net income									(1,367)	(1,332)	(231)
Amounts Reclassified from AOCI | Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax (benefit) provision									(201)	(433)	419
Net income									(319)	(693)	715
Interest income									(520)	(1,126)	1,134
Amounts Reclassified from AOCI | Pension and postretirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax									(40,764)	(38,526)	(44,131)
Tax (benefit) provision									(13,936)	(14,430)	(15,966)
Net income									(26,828)	(24,096)	(28,165)
Transition asset									8	8	9
Prior service costs									(166)	(164)	(171)
Actuarial losses									$ (40,606)	$ (38,370)	$ (43,969)