Loans and Allowance for Credit Losses - Loans by class and credit quality indicators (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 7,760,212		$ 7,545,748
Pass
Loans and Leases Receivable Disclosure [Line Items]
Loans			7,356,769
Watch
Loans and Leases Receivable Disclosure [Line Items]
Loans			109,313
Special Mention
Loans and Leases Receivable Disclosure [Line Items]
Loans			11,460
Substandard
Loans and Leases Receivable Disclosure [Line Items]
Loans			68,206
Doubtful
Loans and Leases Receivable Disclosure [Line Items]
Loans			0
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,437,433	$ 1,545,906	1,545,906
Commercial | Pass
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,287,899		1,470,636
Commercial | Watch
Loans and Leases Receivable Disclosure [Line Items]
Loans	93,095		38,522
Commercial | Special Mention
Loans and Leases Receivable Disclosure [Line Items]
Loans	26,783		11,460
Commercial | Substandard
Loans and Leases Receivable Disclosure [Line Items]
Loans	29,656		25,288
Commercial | Doubtful
Loans and Leases Receivable Disclosure [Line Items]
Loans			0
Income producing - commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans	3,687,000	3,702,747	3,702,747
Income producing - commercial real estate | Pass
Loans and Leases Receivable Disclosure [Line Items]
Loans	3,084,865		3,667,585
Income producing - commercial real estate | Watch
Loans and Leases Receivable Disclosure [Line Items]
Loans	475,517		16,069
Income producing - commercial real estate | Special Mention
Loans and Leases Receivable Disclosure [Line Items]
Loans	52,182
Income producing - commercial real estate | Substandard
Loans and Leases Receivable Disclosure [Line Items]
Loans	74,436		19,093
Owner occupied - commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans	997,694	985,409	985,409
Owner occupied - commercial real estate | Pass
Loans and Leases Receivable Disclosure [Line Items]
Loans	801,548		925,800
Owner occupied - commercial real estate | Watch
Loans and Leases Receivable Disclosure [Line Items]
Loans	49,504		53,146
Owner occupied - commercial real estate | Special Mention
Loans and Leases Receivable Disclosure [Line Items]
Loans	102,619
Owner occupied - commercial real estate | Substandard
Loans and Leases Receivable Disclosure [Line Items]
Loans	44,023		6,463
Real estate mortgage - residential
Loans and Leases Receivable Disclosure [Line Items]
Loans	76,592	104,221	104,221
Real estate mortgage - residential | Pass
Loans and Leases Receivable Disclosure [Line Items]
Loans	70,273		98,228
Real estate mortgage - residential | Watch
Loans and Leases Receivable Disclosure [Line Items]
Loans	3,423		628
Real estate mortgage - residential | Substandard
Loans and Leases Receivable Disclosure [Line Items]
Loans	2,896		5,365
Construction - commercial and residential
Loans and Leases Receivable Disclosure [Line Items]
Loans	873,261	1,035,754	1,125,244
Construction - commercial and residential | Pass
Loans and Leases Receivable Disclosure [Line Items]
Loans	823,020		1,113,734
Construction - commercial and residential | Watch
Loans and Leases Receivable Disclosure [Line Items]
Loans	47,128
Construction - commercial and residential | Special Mention
Loans and Leases Receivable Disclosure [Line Items]
Loans	2,907
Construction - commercial and residential | Substandard
Loans and Leases Receivable Disclosure [Line Items]
Loans	206		11,510
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Loans	73,167	80,061	80,061
Home equity | Pass
Loans and Leases Receivable Disclosure [Line Items]
Loans	70,921		78,626
Home equity | Watch
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,596		948
Home equity | Substandard
Loans and Leases Receivable Disclosure [Line Items]
Loans	650		487
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,389	$ 2,160	2,160
Other consumer | Pass
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,382		$ 2,160
Other consumer | Substandard
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 7