Other Noncurrent Liabilities - Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Payables and Accruals [Abstract]
Benefit plan liabilities	$ 179,473	$ 168,539	$ 206,200
Noncurrent tax liabilities	122,425	124,330	96,083
Other	141,951	191,257	150,001
Total other noncurrent liabilities	$ 443,849	$ 484,126	$ 452,284