Parent company only financial statements - Income Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income
Other interest income	$ 4,051	$ 2,126	$ 1,554
(Loss) gain from other assets	(104)	328	(664)
Net interest income	226,036	204,068	153,271
Interest expense
Interest expense	56,501	35,503	16,342
Other noninterest expense	146,653	121,200	117,461
Net income	83,814	80,236	52,398
Parent Company
Income
Other interest income	0	0	41
Other interest income	0	0	(945)
(Loss) gain from other assets	(16)	297	0
Other income	211	0	0
Net interest income	195	297	(904)
Interest expense
Interest expense	1,638	1,651	1,491
Other noninterest expense	1,056	1,481	893
Other noninterest expense	120	960	296
Federal and state income tax benefit	2,814	4,092	2,680
Loss before income tax benefit and equity in undistributed earnings of bank subsidiary	(2,619)	(3,795)	(3,584)
Federal and state income tax benefit	(683)	(746)	(1,269)
Loss before equity in undistributed earnings of bank subsidiary	(1,936)	(3,049)	(2,315)
Earnings from Bank subsidiary	85,750	83,285	54,713
Net income	$ 83,814	$ 80,236	$ 52,398