Loans and Leases and Allowance for Credit Losses - Aging of amortized cost basis in loans by aging category and accrual status (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Loans by aging category
Total loans	$ 8,935,424	$ 8,812,553
Commercial | Owner occupied commercial real estate
Loans by aging category
Total loans	1,702,984
Commercial | Income producing commercial real estate
Loans by aging category
Total loans	2,064,502
Commercial | Commercial & industrial
Loans by aging category
Total loans	1,310,112
Commercial | Construction
Loans by aging category
Total loans	959,318
Commercial | Equipment financing
Loans by aging category
Total loans	760,952
Residential | Construction
Loans by aging category
Total loans	215,996
Residential | Residential mortgage
Loans by aging category
Total loans	1,127,988
Residential | Home equity lines of credit
Loans by aging category
Total loans	668,382
Consumer
Loans by aging category
Total loans	125,190
Loans receivable
Loans by aging category
Current Loans	8,869,536	8,712,667
Nonaccrual Loans	36,208	35,341
Total loans	8,935,424	8,812,553
Loans receivable | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	25,583
Loans receivable | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	4,097
Loans receivable | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Commercial
Loans by aging category
Current Loans	6,759,360	6,596,675
Nonaccrual Loans	19,972	20,503
Total loans	6,797,868	6,669,593
Loans receivable | Commercial | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	15,660
Loans receivable | Commercial | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	2,876
Loans receivable | Commercial | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Commercial | Owner occupied commercial real estate
Loans by aging category
Current Loans	1,686,758	1,700,682
Nonaccrual Loans	10,405	10,544
Total loans	1,702,984	1,720,227
Loans receivable | Commercial | Owner occupied commercial real estate | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	4,364
Loans receivable | Commercial | Owner occupied commercial real estate | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	1,457
Loans receivable | Commercial | Owner occupied commercial real estate | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Commercial | Income producing commercial real estate
Loans by aging category
Current Loans	2,057,775	1,979,053
Nonaccrual Loans	2,235	1,996
Total loans	2,064,502	2,007,950
Loans receivable | Commercial | Income producing commercial real estate | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	4,482
Loans receivable | Commercial | Income producing commercial real estate | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	10
Loans receivable | Commercial | Income producing commercial real estate | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Commercial | Commercial & industrial
Loans by aging category
Current Loans	1,304,689	1,215,581
Nonaccrual Loans	3,169	2,545
Total loans	1,310,112	1,220,657
Loans receivable | Commercial | Commercial & industrial | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	2,004
Loans receivable | Commercial | Commercial & industrial | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	250
Loans receivable | Commercial | Commercial & industrial | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Commercial | Construction
Loans by aging category
Current Loans	956,397	966,833
Nonaccrual Loans	1,724	2,277
Total loans	959,318	976,215
Loans receivable | Commercial | Construction | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	791
Loans receivable | Commercial | Construction | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	406
Loans receivable | Commercial | Construction | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Commercial | Equipment financing
Loans by aging category
Current Loans	753,741	734,526
Nonaccrual Loans	2,439	3,141
Total loans	760,952	744,544
Loans receivable | Commercial | Equipment financing | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	4,019
Loans receivable | Commercial | Equipment financing | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	753
Loans receivable | Commercial | Equipment financing | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Residential | Construction
Loans by aging category
Current Loans	214,568	235,211
Nonaccrual Loans	540	939
Total loans	215,996	236,437
Loans receivable | Residential | Construction | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	836
Loans receivable | Residential | Construction | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	52
Loans receivable | Residential | Construction | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Residential | Residential mortgage
Loans by aging category
Current Loans	1,110,031	1,097,999
Nonaccrual Loans	12,458	10,567
Total loans	1,127,988	1,117,616
Loans receivable | Residential | Residential mortgage | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	4,882
Loans receivable | Residential | Residential mortgage | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	617
Loans receivable | Residential | Residential mortgage | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Residential | Home equity lines of credit
Loans by aging category
Current Loans	661,857	655,762
Nonaccrual Loans	3,010	3,173
Total loans	668,382	660,675
Loans receivable | Residential | Home equity lines of credit | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	3,223
Loans receivable | Residential | Home equity lines of credit | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	292
Loans receivable | Residential | Home equity lines of credit | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	0
Loans receivable | Consumer
Loans by aging category
Current Loans	123,720	127,020
Nonaccrual Loans	228	159
Total loans	125,190	$ 128,232
Loans receivable | Consumer | Loans Past Due, 30 - 59 Days
Loans by aging category
Loans Past Due	982
Loans receivable | Consumer | Loans Past Due, 60 - 89 Days
Loans by aging category
Loans Past Due	260
Loans receivable | Consumer | Loans Past Due, over 90 Days
Loans by aging category
Loans Past Due	$ 0