Employee Retirement Plans - Narratives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Employer Identification Number	04-6002575
Supplemental Employee Retirement Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Accumulated Benefit Obligation	$ 22,700	$ 18,300
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	811
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	$ 27
Multiemployer Plans, Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Multiemployer Plan Number	333
Pentegra Defined Benefit Plan, Voluntary Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Multiemployer Plan, Voluntary Contributions	$ 6,000	6,000	$ 6,200
Thrift Benefit Equalization Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred Compensation Arrangement with Individual, Recorded Liability	$ 12,600	$ 9,700