Employee Benefit Plans - Defined Benefit Plans - Weighted-Average Asset Allocations (Details) - The Bank - Cash Balance Plan	Dec. 31, 2018	Dec. 31, 2017
Weighted average asset allocations by asset category
Weighted average asset allocation by asset category	100.00%	100.00%
Mutual funds-fixed income
Weighted average asset allocations by asset category
Weighted average asset allocation by asset category	42.00%	39.00%
Mutual funds-equity
Weighted average asset allocations by asset category
Weighted average asset allocation by asset category	58.00%	61.00%