Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	$ 2,431	$ 2,525	$ 7,291	$ 7,203
Pension Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	18	174	52	522
Pension Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	2,044	1,840	6,132	5,429
Expected return on plan assets	(1,195)	(1,318)	(3,585)	(3,797)
Recognized net actuarial loss	1,564	1,829	4,692	5,049
Other Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	180	265	544	845
Other Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	160	80	478	505
Other Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	203	293	615	662
Prior service credit	(107)	$ (108)	(321)	$ (322)
Recognized net actuarial loss	$ (76)		$ (228)