Mergers and acquisitions - Business Acquisition, Pro Forma Information (Details) - Atlantic Capital Bank - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Acquisition [Line Items]
Net interest income	$ 57,023	$ 55,609	$ 113,610	$ 108,687
Total revenues	90,002	92,237	176,413	179,411
Net income	$ 18,688	$ 21,843	$ 37,191	$ 41,474