Qualified Employee Benefit Plans - Net (Benefit) Expense Under the Retirement Plan (Details) - Retirement Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost on projected benefit obligations	$ 4,771	$ 4,999	$ 4,972
Expected return on plan assets	(5,893)	(5,261)	(5,407)
Amortization of prior service cost	24	24	24
Recognized actuarial loss	1,146	1,097	959
Net pension expense	$ 48	$ 859	$ 548