Parent company only financial statements - Income Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income
Other interest income	$ 2,126	$ 1,554	$ 611
Gain (loss) from other assets	328	(664)	(103)
Net interest income	204,068	153,271	110,950
Expenses
Interest expense	35,503	16,342	9,544
Other noninterest expense	32,584	28,035	22,551
Net income	80,236	52,398	40,591
Parent Company
Income
Other interest income	0	41	33
Interest income from Bank subsidiary	0	0	95
(Loss) gain on investments	0	(945)	417
Gain (loss) from other assets	297	0	0
Dividend income from Bank subsidiary	0	0	14,875
Earnings from Bank subsidiary	83,285	54,713	26,859
Net interest income	83,582	53,809	42,279
Expenses
Interest expense	1,651	1,491	1,393
Salaries, legal and professional fees	1,481	893	315
Other noninterest expense	960	296	168
Federal and state income tax benefit	(746)	(1,269)	(188)
Total expenses	3,346	1,411	1,688
Net income	$ 80,236	$ 52,398	$ 40,591