Employee 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
Defined Benefit Plan Disclosure [Line Items]
Settlement expense				$ 19,900
Defined pension plan benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	$ 38	$ 35	$ 112	105
Interest cost on projected benefit obligations	8	6	26	323
Amortization of prior service cost (benefit)	0	0	0	0
Amortization of net loss (benefit)	9	13	27	302
Settlement expense	0	11,732	0	19,900
Net periodic benefit cost	55	11,786	165	19,795
Expected return on plan assets			0	(835)
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost – benefits earned during the year	25	31	77	93
Interest cost on projected benefit obligations	53	47	158	142
Amortization of prior service cost (benefit)	0	(3)	0	(10)
Amortization of net loss (benefit)	(29)	(8)	(88)	(23)
Settlement expense	0	0	0	0
Net periodic benefit cost	$ 49	$ 67	147	202
Expected return on plan assets			$ 0	$ 0