Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accrued Expenses
Salaries and wages	$ 100,273	$ 90,913
Deferred compensation	3,990	2,992
Pension benefits	3,842	3,796
Other postretirement benefits	1,520	1,506
Other employee benefits	22,678	29,358
Insurance obligations	133,855	127,470
Asset retirement obligations	6,595	5,828
Operating taxes	99,086	92,150
Income taxes	2,570	4,197
Interest	26,066	27,277
Customer deposits	66,302	61,225
Deferred revenue	14,997	14,064
Other	47,397	46,413
Total	529,171	507,189
Non-Current Liabilities
Salaries and wages	0	0
Deferred compensation	54,595	46,541
Pension benefits	462,935	451,940
Other postretirement benefits	19,163	19,459
Other employee benefits	2,958	5,854
Insurance obligations	261,244	234,336
Asset retirement obligations	19,810	20,143
Operating taxes	0	0
Income taxes	24,623	23,174
Interest	0	0
Customer deposits	4,089	4,569
Deferred revenue	0	0
Other	22,654	11,549
Total	872,071	817,565
Total
Salaries and wages	100,273	90,913
Deferred compensation	58,585	49,533
Pension benefits	466,777	455,736
Other postretirement benefits	20,683	20,965
Other employee benefits	25,636	35,212
Insurance obligations	395,099	361,806
Asset retirement obligations	26,405	25,971
Operating taxes	99,086	92,150
Income taxes	27,193	27,371
Interest	26,066	27,277
Customer deposits	70,391	65,794
Deferred revenue	14,997	14,064
Other	70,051	57,962
Total	$ 1,401,242	$ 1,324,754