Mergers and acquisitions - Business Acquisition, Pro Forma Information (Details) - Atlantic Capital Bank - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition [Line Items]
Net interest income	$ 58,305	$ 56,522	$ 171,915	$ 165,209
Total revenues	96,450	91,688	272,868	271,099
Net income	$ 23,966	$ 20,283	$ 59,745	$ 60,680