Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating activities
Net income	$ 144,678,000	$ 166,068,000	$ 175,892,000
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for (recovery of) credit losses	15,593,000	23,871,000	(2,168,000)
Depreciation, amortization and accretion	35,231,000	42,744,000	47,350,000
Deferred income tax (benefit) expense	(5,005,000)	2,280,000	11,411,000
Impairment losses on securities	19,352,000	0	0
Proceeds from sale of mortgage servicing rights	0	18,525,000	0
Gain on sale of mortgage servicing rights	(547,000)	(2,960,000)	0
Funding of mortgage loans held for sale	(1,330,912,000)	(1,679,356,000)	(4,059,927,000)
Proceeds from sales of mortgage loans held for sale	1,277,363,000	2,043,360,000	4,116,106,000
Gains on sales of mortgage loans held for sale	(14,573,000)	(15,803,000)	(82,399,000)
Valuation adjustment to mortgage servicing rights	0	0	(13,561,000)
Losses (gains) on sales of securities	22,438,000	0	(2,170,000)
Debt prepayment penalty	0	0	6,123,000
Gain on debt extinguishment	(620,000)	0	0
Gains on sales of premises and equipment	(173,000)	(239,000)	(840,000)
Stock-based compensation	13,716,000	11,505,000	10,074,000
Increase in other assets	(51,986,000)	(29,671,000)	(20,812,000)
Increase (decrease) in other liabilities	23,998,000	(6,279,000)	(42,420,000)
Net cash provided by operating activities	148,553,000	574,045,000	142,659,000
Investing activities
Purchases of securities available for sale	(11,899,000)	(713,096,000)	(2,107,934,000)
Proceeds from sales of securities available for sale	488,981,000	0	176,455,000
Proceeds from call/maturities of securities available for sale	149,025,000	385,507,000	458,020,000
Purchases of securities held to maturity	0	(91,803,000)	(52,135,000)
Proceeds from call/maturities of securities held to maturity	109,953,000	67,448,000	2,246,000
Net (increase) decrease in loans	(791,803,000)	(1,456,119,000)	910,063,000
Purchases of premises and equipment	(21,634,000)	(14,838,000)	(20,516,000)
Proceeds from sales of premises and equipment	943,000	1,234,000	9,813,000
Purchase of bank-owned life insurance	0	(80,000,000)	(50,000,000)
Net change in FHLB stock	16,076,000	(27,807,000)	3,980,000
Proceeds from sales of other assets	3,115,000	3,578,000	6,342,000
Net cash paid in acquisitions	0	(120,888,000)	0
Other, net	1,844,000	3,127,000	3,663,000
Net cash used in investing activities	(55,399,000)	(2,043,657,000)	(660,003,000)
Financing activities
Net (decrease) increase in noninterest-bearing deposits	(975,081,000)	(159,368,000)	1,033,076,000
Net increase (decrease) in interest-bearing deposits	1,564,900,000	(259,390,000)	813,567,000
Net (decrease) increase in short-term borrowings	(404,655,000)	668,805,000	(7,393,000)
Proceeds from long-term debt	0	0	197,061,000
Repayment of long-term debt	(2,680,000)	(32,417,000)	(202,873,000)
Cash paid for dividends	(50,279,000)	(49,991,000)	(50,017,000)
Repurchase of shares in connection with stock repurchase program	0	0	(21,315,000)
Net cash provided by financing activities	132,205,000	167,639,000	1,762,106,000
Net increase (decrease) in cash and cash equivalents	225,359,000	(1,301,973,000)	1,244,762,000
Cash and cash equivalents at beginning of year	575,992,000	1,877,965,000	633,203,000
Cash and cash equivalents at end of year	801,351,000	575,992,000	1,877,965,000
Supplemental disclosures
Cash paid for interest	239,611,000	54,562,000	45,745,000
Cash paid for income taxes	42,047,000	41,764,000	50,977,000
Noncash transactions:
Transfers of loans to other real estate	10,738,000	2,207,000	3,180,000
Financed sales of other real estate owned	0	0	577,000
Recognition of operating right-of-use assets	3,126,000	3,475,000	8,142,000
Recognition of operating lease liabilities	3,126,000	3,475,000	8,142,000
Available for sale securities transferred to held to maturity securities	$ 0	$ 882,927,000	$ 366,886,000