Disclosures about Fair Value of Assets and Liabilities - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial assets:
Loans held for sale	$ 41,418	$ 19,592
Carrying Value
Financial assets:
Cash and cash equivalents	429,202	506,709
Securities purchased under agreements to resell	6,616	6,723
FHLB stock	70,656	20,369
Loans held for sale	3,278,201	2,074,197
Loans, net	4,857,554	3,012,468
Interest receivable	19,130	18,359
Financial liabilities:
Deposits	7,084,647	5,478,075
Lines of credit		6,540
Short-term subordinated debt	14,960	12,200
FHLB advances	1,221,130	162,699
Federal Reserve discount window/PPPLF advances	382,111
Interest payable	3,968	11,938
Fair Value
Financial assets:
Cash and cash equivalents	429,202	506,709
Securities purchased under agreements to resell	6,616	6,723
FHLB stock	70,656	20,369
Loans held for sale	3,278,201	2,074,197
Loans, net	4,847,874	2,999,580
Interest receivable	19,130	18,359
Financial liabilities:
Deposits	7,087,928	5,478,682
Lines of credit		6,540
Short-term subordinated debt	14,960	12,200
FHLB advances	1,221,371	162,803
Federal Reserve discount window/PPPLF advances	382,111
Interest payable	3,968	11,938
Level 1 | Fair Value
Financial assets:
Cash and cash equivalents	429,202	506,709
Financial liabilities:
Deposits	5,897,805	3,303,736
Level 2 | Fair Value
Financial assets:
Securities purchased under agreements to resell	6,616	6,723
FHLB stock	70,656	20,369
Loans held for sale	3,278,201	2,074,197
Interest receivable	19,130	18,359
Financial liabilities:
Deposits	1,190,123	2,174,946
Lines of credit		6,540
Short-term subordinated debt	14,960	12,200
FHLB advances	1,221,371	162,803
Federal Reserve discount window/PPPLF advances	382,111
Interest payable	3,968	11,938
Level 3 | Fair Value
Financial assets:
Loans, net	$ 4,847,874	$ 2,999,580