Description of Business and Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Standards Update 2017-07 [Member]
Defined Benefit Plan, Other Cost (Credit)	$ (5,800)	$ (8,600)	$ 2,400
Minimum [Member]
Increase in assets due to ASU 2016-02	150,000
Maximum [Member]
Increase in assets due to ASU 2016-02	$ 200,000