Other Assets (Details) - Composition of Other Assets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Benefit plan-related assets	$ 97,525	$ 45,958
Non-current deferred tax assets	31,067	27,275
Other	65,150	14,046
Total other assets	$ 193,742	$ 87,279