Investments - Available-for-sale securities reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost	$ 153,098	$ 125,053
Unrealized gains	3,698	1,347
Unrealized losses	(330)	(343)
Securities available-for-sale, at fair value	156,466	126,057
U.S. agency securities
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost	6,991	8,986
Unrealized gains	136	95
Unrealized losses		(15)
Securities available-for-sale, at fair value	7,127	9,066
Corporate securities
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost	19,858	10,525
Unrealized gains	144	52
Unrealized losses	(151)	(7)
Securities available-for-sale, at fair value	19,851	10,570
Municipal bonds
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost	31,062	20,516
Unrealized gains	475	604
Unrealized losses	(131)
Securities available-for-sale, at fair value	31,406	21,120
Mortgage-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost	74,503	62,745
Unrealized gains	2,271	405
Unrealized losses	(41)	(300)
Securities available-for-sale, at fair value	76,733	62,850
U.S. Small Business Administration securities
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost	20,684	22,281
Unrealized gains	672	191
Unrealized losses	(7)	(21)
Securities available-for-sale, at fair value	$ 21,349	$ 22,451