Business Combinations - Business Acquisition, Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net interest income		$ 60,159	$ 35,683	$ 177,131	$ 104,843
Provision for credit losses	[1]	3,658	1,327	49,312	1,821
Non-interest income		50,477	27,627	102,024	84,390
Non-interest expense		43,563	23,265	123,856	72,364
Income before income taxes		31,914	16,204	40,181	45,167
Income tax expense		$ 6,259	$ 3,033	7,951	8,315
Pro Forma [Member]
Net interest income				160,955	159,818
Provision for credit losses				25,059	2,473
Non-interest income				65,295	52,630
Non-interest expense				115,420	125,091
Income before income taxes				85,771	84,884
Income tax expense				17,515	15,607
Net income				$ 68,256	$ 69,277
Diluted earnings per share				$ 1.82	$ 1.82

[1] Beginning January 1, 2020, calculation is based on current expected loss methodology.  Prior to January 1, 2020, calculation was based on incurred loss methodology.