Derivatives, Hedging Activities, and Other Financial Instruments - Notional and Fair Value of Derivatives Assets and Liabilities (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Other assets
Derivative [Line Items]
Derivative asset, notional amount	$ 19,863
Credit risk derivative asset, fair value	415
Other liabilities
Derivative [Line Items]
Derivative liability, notional amount	19,863
Credit risk derivative liability, fair value	$ 416