Acquisitions - Acquisition date fair value of purchased assets and assumed liabilities (Details) - USD ($) $ in Thousands	Jul. 01, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Liabilities
Goodwill		$ 369,018	$ 327,425	$ 327,425	$ 327,425	$ 327,425	$ 307,112
Three Shores
Assets
Cash and cash equivalents	$ 218,714
Debt securities	381,740
Loans, net	1,427,966
Premises and equipment, net	1,584
Accrued interest receivable	7,565
Derivative assets	11,800
Net deferred tax asset	15,061
Core deposit intangible	3,360
Other assets	65,340
Total assets acquired	2,133,130
Liabilities
Deposits	1,802,694
FHLB advances and long-term debt	144,121
Derivative liabilities	12,165
Other liabilities	28,046
Total liabilities assumed	1,987,026
Total identifiable net assets	146,104
Cash consideration transferred	24,108
Common stock issued (8,130,633 shares)	163,589
Total fair value of consideration transferred	187,697
Goodwill	$ 41,593
Common stock issued (in shares)	8,130,633
Three Shores | As Recorded By Three Shores
Assets
Cash and cash equivalents	$ 218,714
Debt securities	374,237
Loans, net	1,463,567
Premises and equipment, net	1,892
Accrued interest receivable	8,849
Derivative assets	12,165
Net deferred tax asset	3,837
Core deposit intangible	0
Other assets	71,984
Total assets acquired	2,155,245
Liabilities
Deposits	1,796,739
FHLB advances and long-term debt	136,000
Derivative liabilities	12,165
Other liabilities	30,857
Total liabilities assumed	1,975,761
Total identifiable net assets	179,484
Three Shores | Fair Value Adjustments
Assets
Cash and cash equivalents	0
Debt securities	7,503
Loans, net	(35,601)
Premises and equipment, net	(308)
Accrued interest receivable	(1,284)
Derivative assets	(365)
Net deferred tax asset	11,224
Core deposit intangible	3,360
Other assets	(6,644)
Total assets acquired	(22,115)
Liabilities
Deposits	5,955
FHLB advances and long-term debt	8,121
Derivative liabilities	0
Other liabilities	(2,811)
Total liabilities assumed	11,265
Aggregate fair value adjustments	$ (33,380)