Fair Value Measurements Fair Value, Assets Measured on Recurring Basis, Valuation Techniques (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($)		Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities	$ 416		$ 0
Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights	209		181
Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights	209		181
Equity securities	416
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights	209		181
Equity securities	416
Fair Value, Measurements, Recurring | Other investments | Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			$ 433	$ 403	$ 391
Fair Value Measurements, Valuation Processes, Description			Cost
Fair Value, Measurements, Recurring | Equity Investments | Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 416		$ 433
Fair Value Measurements, Valuation Processes, Description	Cost
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description	n/a			n/a
Fair Value, Measurements, Recurring | Other Assets | Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 209		$ 181	$ 192	$ 183
Fair Value Measurements, Valuation Processes, Description	Discounted Cash Flow		Discounted Cash Flow
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description	Weighted Average Constant Prepayment Rate(1)	[1]	Weighted Average Constant Prepayment Rate(1)
Servicing Asset, Measurement Input	0.0928		0.2003

[1] (1) Represents annualized loan repayment rate assumptions