Loans and Leases and Allowance for Credit Losses - Major classifications of loans (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Classifications of loans
Total loans	$ 8,935,424	$ 8,812,553
Less allowance for credit losses - loans	(81,905)	(62,089)	$ (61,642)	$ (61,203)
Loans and leases, net	8,853,519	8,750,464
Commercial | Owner occupied commercial real estate
Classifications of loans
Total loans	1,702,984
Commercial | Income producing commercial real estate
Classifications of loans
Total loans	2,064,502
Commercial | Commercial & industrial
Classifications of loans
Total loans	1,310,112
Commercial | Construction
Classifications of loans
Total loans	959,318
Commercial | Equipment financing
Classifications of loans
Total loans	760,952
Residential | Residential mortgage
Classifications of loans
Total loans	1,127,988
Residential | Home equity lines of credit
Classifications of loans
Total loans	668,382
Residential | Construction
Classifications of loans
Total loans	215,996
Consumer
Classifications of loans
Total loans	125,190
Loans receivable
Classifications of loans
Total loans	8,935,424	8,812,553
Loans receivable | Commercial
Classifications of loans
Total loans	6,797,868	6,669,593
Loans receivable | Commercial | Owner occupied commercial real estate
Classifications of loans
Total loans	1,702,984	1,720,227
Less allowance for credit losses - loans	(11,000)	(11,404)	(11,874)	(12,207)
Loans receivable | Commercial | Income producing commercial real estate
Classifications of loans
Total loans	2,064,502	2,007,950
Less allowance for credit losses - loans	(16,584)	(12,306)	(11,126)	(11,073)
Loans receivable | Commercial | Commercial & industrial
Classifications of loans
Total loans	1,310,112	1,220,657
Less allowance for credit losses - loans	(10,831)	(5,266)	(4,895)	(4,802)
Loans receivable | Commercial | Construction
Classifications of loans
Total loans	959,318	976,215
Less allowance for credit losses - loans	(9,556)	(9,668)	(10,275)	(10,337)
Loans receivable | Commercial | Equipment financing
Classifications of loans
Total loans	760,952	744,544
Less allowance for credit losses - loans	(14,738)	(7,384)	(6,231)	(5,452)
Loans receivable | Residential | Residential mortgage
Classifications of loans
Total loans	1,127,988	1,117,616
Less allowance for credit losses - loans	(11,063)	(8,081)	(8,345)	(8,295)
Loans receivable | Residential | Home equity lines of credit
Classifications of loans
Total loans	668,382	660,675
Less allowance for credit losses - loans	(6,887)	(4,575)	(4,797)	(4,752)
Loans receivable | Residential | Construction
Classifications of loans
Total loans	215,996	236,437
Less allowance for credit losses - loans	(816)	(2,504)	(2,390)	(2,433)
Loans receivable | Consumer
Classifications of loans
Total loans	125,190	128,232
Less allowance for credit losses - loans	$ (430)	$ (901)	$ (837)	$ (853)