Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Settlement expense				$ 8,168
Defined pension plan benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	$ 37	$ 41	$ 74	70
Interest cost on projected benefit obligations	9	222	18	317
Expected return on plan assets	0	(591)	0	(835)
Amortization of prior service cost (benefit)	0	0	0	0
Amortization of net loss (benefit)	9	201	18	289
Settlement expense	0	8,168	0	8,168
Net periodic benefit cost	55	8,041	110	8,009
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	23	28	52	62
Interest cost on projected benefit obligations	51	47	105	95
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (benefit)	0	(15)	0	(7)
Amortization of net loss (benefit)	(34)	0	(59)	(15)
Settlement expense	0	0	0	0
Net periodic benefit cost	$ 40	$ 60	$ 98	$ 135