Other Assets - Composition of Other Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Benefit plan-related assets	$ 75,653	$ 97,525
Non-current deferred tax assets	34,494	31,067
Other	46,222	65,150
Total other assets	$ 156,369	$ 193,742