Retirement Plans - Non-contributory defined benefit pension plan (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jun. 30, 2019	Sep. 30, 2019
Retirement Plans
Pension plan termination expense	$ 9,500	$ 9,526
Recognition of pre-tax losses from pension plan		(7,700)
Write-off of pension plan asset		$ 1,800
Non-contributory defined benefit pension plan | Employees hired on or before December 31, 2005
Retirement Plans
Requisite age of employees for receiving retirement benefits under the plan		21 years
Non-contributory defined benefit pension plan | Employee hired on or after January 1, 2006
Retirement Plans
Requisite age of employees for receiving retirement benefits under the new benefit formula		45 years
Requisite age of employees for receiving retirement benefits under the new benefit formula		5 years