Fair Value Measurements - Not Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
FINANCIAL ASSETS:
Investment securities held-to-maturity	$ 32,631	$ 35,942
Book Value
FINANCIAL ASSETS:
Cash and cash equivalents	1,389,943	1,055,588
Investment securities held-to-maturity	31,943	35,223
Loans held for sale	8,434	17,421
Loans, net	7,142,315	7,023,071
Other financial assets	56,917	57,654
FINANCIAL LIABILITIES:
Deposits	9,147,618	8,595,366
Securities sold under agreements to repurchase	46,262	53,472
Federal Home Loan Bank borrowings	115,019	114,659
Junior subordinated debentures	106,363	106,363
Other financial liabilities	1,751	1,734
Fair Value
FINANCIAL ASSETS:
Cash and cash equivalents	1,389,943	1,055,588
Investment securities held-to-maturity	32,631	35,942
Loans held for sale	8,431	17,782
Loans, net	7,035,003	6,980,202
Other financial assets	56,917	57,654
FINANCIAL LIABILITIES:
Deposits	9,148,568	8,596,193
Securities sold under agreements to repurchase	46,262	53,472
Federal Home Loan Bank borrowings	115,410	115,284
Junior subordinated debentures	69,863	69,863
Other financial liabilities	1,751	1,734
Fair Value | Quoted prices in active markets for identical assets (Level 1)
FINANCIAL ASSETS:
Cash and cash equivalents	1,389,943	1,055,588
Investment securities held-to-maturity	0	0
Loans held for sale	0	0
Loans, net	0	0
Other financial assets	0	0
FINANCIAL LIABILITIES:
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Federal Home Loan Bank borrowings	0	0
Junior subordinated debentures	0	0
Other financial liabilities	0	0
Fair Value | Significant  other observable inputs (Level 2)
FINANCIAL ASSETS:
Cash and cash equivalents	0	0
Investment securities held-to-maturity	32,631	35,942
Loans held for sale	8,431	17,782
Loans, net	0	0
Other financial assets	56,917	57,654
FINANCIAL LIABILITIES:
Deposits	9,148,568	8,596,193
Securities sold under agreements to repurchase	46,262	53,472
Federal Home Loan Bank borrowings	115,410	115,284
Junior subordinated debentures	0	0
Other financial liabilities	1,751	1,734
Fair Value | Significant unobservable inputs (Level 3)
FINANCIAL ASSETS:
Cash and cash equivalents	0	0
Investment securities held-to-maturity	0	0
Loans held for sale	0	0
Loans, net	7,035,003	6,980,202
Other financial assets	0	0
FINANCIAL LIABILITIES:
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Federal Home Loan Bank borrowings	0	0
Junior subordinated debentures	69,863	69,863
Other financial liabilities	$ 0	$ 0