Fair Value Measurements - Assets and Liabilities Not Measured and Reported at Fair Value on a Recurring Basis or Nonrecurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Dec. 31, 2024
Financial assets
Securities held to maturity	$ 928,696	$ 961,870
Securities available for sale	2,809,647	2,560,818
Loans held for sale	230,980	265,959
Mortgage servicing rights	64,850	65,271	$ 72,902	$ 72,991
Derivative instruments	25,018	21,867
Financial liabilities
Derivative instruments	18,470	17,650
Carrying Value
Financial assets
Cash and cash equivalents	1,216,980	1,070,718
Securities held to maturity	1,006,511	1,030,073
Securities available for sale	2,809,647	2,560,818
Loans held for sale	230,980	265,959
Loans, net	18,679,386	18,753,084
Mortgage servicing rights	64,850	65,271
Derivative instruments	43,578	47,098
Financial liabilities
Deposits	22,099,484	21,473,070
Short-term borrowings	305,863	555,774
Junior subordinated debentures	140,908	140,632
Subordinated notes	359,434	359,124
Derivative instruments	35,553	41,484
Fair Value
Financial assets
Cash and cash equivalents	1,216,980	1,070,718
Securities held to maturity	928,696	961,870
Securities available for sale	2,809,647	2,560,818
Loans held for sale	230,980	265,959
Loans, net	18,575,666	18,689,957
Mortgage servicing rights	85,082	80,537
Derivative instruments	43,578	47,098
Financial liabilities
Deposits	22,091,013	21,465,168
Short-term borrowings	305,863	555,774
Junior subordinated debentures	126,976	126,976
Subordinated notes	351,755	352,616
Derivative instruments	35,553	41,484
Fair Value | Level 1
Financial assets
Cash and cash equivalents	1,216,980	1,070,718
Securities held to maturity	0	0
Securities available for sale	0	0
Loans held for sale	0	0
Loans, net	0	0
Mortgage servicing rights	0	0
Derivative instruments	0	0
Financial liabilities
Deposits		0
Short-term borrowings	0	0
Junior subordinated debentures	0	0
Subordinated notes	0	0
Derivative instruments	0	0
Fair Value | Level 2
Financial assets
Cash and cash equivalents	0	0
Securities held to maturity	928,696	961,870
Securities available for sale	2,809,647	2,560,818
Loans held for sale	230,980	265,959
Loans, net	0	0
Mortgage servicing rights	0	0
Derivative instruments	43,578	47,098
Financial liabilities
Deposits	22,091,013	21,465,168
Short-term borrowings	305,863	555,774
Junior subordinated debentures	126,976	126,976
Subordinated notes	351,755	352,616
Derivative instruments	35,553	41,484
Fair Value | Level 3
Financial assets
Cash and cash equivalents	0	0
Securities held to maturity	0	0
Securities available for sale	0	0
Loans held for sale	0	0
Loans, net	18,575,666	18,689,957
Mortgage servicing rights	85,082	80,537
Derivative instruments	0	0
Financial liabilities
Deposits	0	0
Short-term borrowings	0	0
Junior subordinated debentures	0	0
Subordinated notes	0	0
Derivative instruments	$ 0	$ 0