Investment Securities - Additional Information (Detail) Securities in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2022 USD ($) Securities	Dec. 31, 2021 USD ($)
Schedule of Investments [Line Items]
Accrued interest receivable	$ 20,039	$ 15,353
Gross unrealized losses on available for sale securities	$ 341,906	34,417
Available for sale securities in unrealized loss position | Securities	1,374
Available for sale securities in portfolio, number | Securities	1,543
Amortized cost of available for sale securities	$ 5,153,285	4,031,494
Capitalization of banks, equal to or greater than, in the single-issue trust preferred portfolio	10,000,000
Equity securities at estimated fair value	13,513	12,404
Carrying value of securities pledged	$ 1,636,234	1,871,328
Fitch, AAA Rating [Member]
Schedule of Investments [Line Items]
Percentage of asset backed securities with credit rating	69.00%
Federal Family Education Loan Program [Member] | Fitch, AA+ Rating [Member]
Schedule of Investments [Line Items]
Percentage of asset backed securities with credit rating	31.00%
Percentage Of Asset Backed Securities With investment grade	100.00%
Minimum [Member] | Federal Family Education Loan Program [Member] | Fitch, AA+ Rating [Member]
Schedule of Investments [Line Items]
Percentage of repayment guaranteed by the government	97.00%
Non Agency Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale securities	$ 114,692
Investment Grade [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale single issue trust preferred securities	8,461
Split Rated Bonds Investment Grade [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale single issue trust preferred securities	3,078
Unrated Bonds Investment Grade [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale single issue trust preferred securities	5,777
State and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	85,785	3,809
Amortized cost of available for sale securities	$ 836,622	831,499
Percent of portfolio with credit support	53.00%
Agency Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale securities	$ 2,111,407
Commercial Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	44,897	6,608
Amortized cost of available for sale securities	686,470	633,802
Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	130,114	15,822
Amortized cost of available for sale securities	1,424,937	1,120,423
Residential Mortgage-Backed Securities, Non-agency [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	6,252	726
Amortized cost of available for sale securities	114,692	74,965
Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Recognized in Earnings	$ 0
Residential Mortgage-Backed Securities, Non-agency [Member] | AAA [Member]
Schedule of Investments [Line Items]
Percentage of asset backed securities with credit rating	100.00%
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	$ 27,997	3,182
Amortized cost of available for sale securities	$ 617,171	611,548
Corporate Bonds [Member] | Investment Grade [Member]
Schedule of Investments [Line Items]
Percent of corporate securities portfolio	96.00%
Percent Of Corporate Securities Portfolio	96.00%
Corporate Bonds [Member] | Below Investment Grade [Member]
Schedule of Investments [Line Items]
Percent of corporate securities portfolio	2.00%
Percent Of Corporate Securities Portfolio	2.00%
Corporate Bonds [Member] | Split Rated Bonds Investment Grade [Member]
Schedule of Investments [Line Items]
Percent of corporate securities portfolio	1.00%
Percent Of Corporate Securities Portfolio	1.00%
Corporate Bonds [Member] | Unrated Bonds Investment Grade [Member]
Schedule of Investments [Line Items]
Percent of corporate securities portfolio	1.00%
Percent Of Corporate Securities Portfolio	1.00%
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	$ 35,738	3,307
Amortized cost of available for sale securities	953,347	$ 659,830
Asset-backed Securities [Member] | Federal Family Education Loan Program [Member] | Fitch, AA+ Rating [Member]
Schedule of Investments [Line Items]
Impairment of investment in asset backed securities	$ 0