Significant Accounting Policies - Impact of new financial accounting standards (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2019	Sep. 30, 2019	Jan. 01, 2019
Recently Issued Accounting Standards
Lease, Practical Expedients, Package [true false]		true
Lease, Practical Expedient, Use of Hindsight [true false]		false
Right of use asset		$ 9,979
Lease liability		$ 10,101
Accounting Standards Update 2017-12
Recently Issued Accounting Standards
Transferred securities from held to maturity to available-for-sale	$ 573,600
Accounting Standards Update 2016-02 | Restatement
Recently Issued Accounting Standards
Right of use asset			$ 8,100
Lease liability			$ 8,100