Loans and Leases and Allowance for Credit Losses - Major classifications of loans (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Classifications of loans
Total loans	$ 11,798,910		$ 8,812,553
Less allowance for credit losses - loans	(134,256)		(62,089)	$ (62,514)		$ (61,203)
Amount of loans	11,664,654		8,750,464
Commercial | Owner occupied commercial real estate
Classifications of loans
Total loans	2,008,674
Commercial | Income producing commercial real estate
Classifications of loans
Total loans	2,493,625
Commercial | Commercial & industrial
Classifications of loans
Total loans	3,104,868
Commercial | Construction
Classifications of loans
Total loans	981,371
Commercial | Equipment financing
Classifications of loans
Total loans	823,022
Residential | Residential mortgage
Classifications of loans
Total loans	1,269,548
Residential | Home equity lines of credit
Classifications of loans
Total loans	706,877
Residential | Construction
Classifications of loans
Total loans	263,266
Consumer
Classifications of loans
Total loans	147,659
Loans receivable
Classifications of loans
Total loans	11,798,910		8,812,553
Less allowance for credit losses - loans	(134,256)	$ (103,669)		(62,514)	$ (62,204)
Loans receivable | Commercial
Classifications of loans
Total loans	9,411,560		6,669,593
Loans receivable | Commercial | Owner occupied commercial real estate
Classifications of loans
Total loans	2,008,674		1,720,227
Less allowance for credit losses - loans	(19,374)	(14,592)	(11,404)	(11,419)	(11,545)	(12,207)
Loans receivable | Commercial | Income producing commercial real estate
Classifications of loans
Total loans	2,493,625		2,007,950
Less allowance for credit losses - loans	(35,038)	(21,699)	(12,306)	(11,062)	(11,020)	(11,073)
Loans receivable | Commercial | Commercial & industrial
Classifications of loans
Total loans	3,104,868		1,220,657
Less allowance for credit losses - loans	(21,524)	(8,589)	(5,266)	(5,390)	(5,308)	(4,802)
Loans receivable | Commercial | PPP loans included in commercial & industrial
Classifications of loans
Total loans	1,320,000
Loans receivable | Commercial | Construction
Classifications of loans
Total loans	981,371		976,215
Less allowance for credit losses - loans	(14,851)	(14,514)	(9,668)	(10,407)	(10,318)	(10,337)
Loans receivable | Commercial | Equipment financing
Classifications of loans
Total loans	823,022		744,544
Less allowance for credit losses - loans	(15,176)	(20,305)	(7,384)	(7,246)	(6,935)	(5,452)
Loans receivable | Residential | Residential mortgage
Classifications of loans
Total loans	1,269,548		1,117,616
Less allowance for credit losses - loans	(17,562)	(12,826)	(8,081)	(8,214)	(8,290)	(8,295)
Loans receivable | Residential | Home equity lines of credit
Classifications of loans
Total loans	706,877		660,675
Less allowance for credit losses - loans	(8,721)	(8,687)	(4,575)	(4,683)	(4,794)	(4,752)
Loans receivable | Residential | Construction
Classifications of loans
Total loans	263,266		236,437
Less allowance for credit losses - loans	(1,768)	(1,997)	(2,504)	(2,551)	(2,365)	(2,433)
Loans receivable | Consumer
Classifications of loans
Total loans	147,659		128,232
Less allowance for credit losses - loans	$ (242)	$ (460)	$ (901)	$ (877)	$ (855)	$ (853)