Loans (Activity in Allowance for Loan Losses by Portfolio Segment) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	$ 227,621
Financing Receivable, Allowance for Credit Loss, Ending Balance	245,996	$ 227,621
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	104,237	72,091	$ 73,843
Financing Receivable, Credit Loss, Expense (Reversal)	(16,709)	34,479	(2,160)
Financing Receivable, Allowance for Credit Loss, Writeoff	(18,315)	(6,575)	(5,513)
Financing Receivable, Allowance for Credit Loss, Recovery	4,793	4,242	5,921
Allowance for Loan and Lease Losses Write-offs, Net	(13,522)	(2,333)	408
Financing Receivable, Allowance for Credit Loss, Ending Balance	74,006	104,237	72,091
Commercial And Industrial Energy Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	18,062	17,217	39,553
Financing Receivable, Credit Loss, Expense (Reversal)	(1,067)	(313)	(19,207)
Financing Receivable, Allowance for Credit Loss, Writeoff	(518)	(371)	(5,331)
Financing Receivable, Allowance for Credit Loss, Recovery	1,337	1,529	2,202
Allowance for Loan and Lease Losses Write-offs, Net	819	1,158	(3,129)
Financing Receivable, Allowance for Credit Loss, Ending Balance	17,814	18,062	17,217
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	90,301	144,936	134,892
Financing Receivable, Credit Loss, Expense (Reversal)	40,889	(54,775)	8,101
Financing Receivable, Allowance for Credit Loss, Writeoff	(955)	(702)	(399)
Financing Receivable, Allowance for Credit Loss, Recovery	363	842	2,342
Allowance for Loan and Lease Losses Write-offs, Net	(592)	140	1,943
Financing Receivable, Allowance for Credit Loss, Ending Balance	130,598	90,301	144,936
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	8,004	6,585	7,926
Financing Receivable, Credit Loss, Expense (Reversal)	6,736	1,813	(3,061)
Financing Receivable, Allowance for Credit Loss, Writeoff	(2,883)	(912)	(829)
Financing Receivable, Allowance for Credit Loss, Recovery	1,681	518	2,549
Allowance for Loan and Lease Losses Write-offs, Net	(1,202)	(394)	1,720
Financing Receivable, Allowance for Credit Loss, Ending Balance	13,538	8,004	6,585
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	7,017	7,837	6,963
Financing Receivable, Credit Loss, Expense (Reversal)	23,012	13,517	10,230
Financing Receivable, Allowance for Credit Loss, Writeoff	(31,260)	(24,388)	(18,614)
Financing Receivable, Allowance for Credit Loss, Recovery	11,271	10,051	9,258
Allowance for Loan and Lease Losses Write-offs, Net	(19,989)	(14,337)	(9,356)
Financing Receivable, Allowance for Credit Loss, Ending Balance	10,040	7,017	7,837
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	227,621	248,666	263,177
Financing Receivable, Credit Loss, Expense (Reversal)	52,861	(5,279)	(6,097)
Financing Receivable, Allowance for Credit Loss, Writeoff	(53,931)	(32,948)	(30,686)
Financing Receivable, Allowance for Credit Loss, Recovery	19,445	17,182	22,272
Allowance for Loan and Lease Losses Write-offs, Net	(34,486)	(15,766)	(8,414)
Financing Receivable, Allowance for Credit Loss, Ending Balance	$ 245,996	$ 227,621	$ 248,666