Employee Benefit Plans - Cost Components of Supplemental Executive Retirement Plan (Details) - SERP - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,933	$ 1,711
Interest cost	470	448
Net pension expense (benefit)	$ 2,403	$ 2,159