Significant Accounting Policies - Impact of new financial accounting standards (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Recently Issued Accounting Standards
Lease, Practical Expedients, Package [true false]		true
Lease, Practical Expedient, Use of Hindsight [true false]		false
Right of use asset		$ 9,490
Lease liability		$ 9,552
Allowance for credit losses | Credit concentration risk | Minimum
Recently Issued Accounting Standards
Percentage increase in reserve for unfunded commitments above the existing allowance for loan loss levels		25
Allowance for credit losses | Credit concentration risk | Maximum
Recently Issued Accounting Standards
Percentage increase in reserve for unfunded commitments above the existing allowance for loan loss levels		45
Accounting Standards Update 2016-02 | Restatement
Recently Issued Accounting Standards
Right of use asset			$ 8,100
Lease liability			$ 8,100
Accounting Standards Update 2017-12
Recently Issued Accounting Standards
Transferred securities from held to maturity to available-for-sale	$ 573,600	$ 0