Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	$ 6,573,179	$ 4,393,029
Loans held-for-sale	37,810	83,969
Obligations of State and Political Subdivisions [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	2,753,471	2,426,876
Residential Mortgage-Backed Securities [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	3,259,449	1,472,280
Commercial Mortgage-Backed Securities [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	365,120	489,316
IRLCs [Member]
Activity in available-for-sale securities and other investments:
Asset Derivative Fair Value	1,279	4,618
Liability Derivative Fair Value	0	0
Forward Mortgage-Backed Securities Trades [Member]
Activity in available-for-sale securities and other investments:
Asset Derivative Fair Value	0	0
Liability Derivative Fair Value	147	1,560
U.S. Treasury securities [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	126,841
Fair Value, Measurements, Recurring [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	6,573,179	4,393,029
Loans held-for-sale	34,122	79,585
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	63,868
Fair Value, Measurements, Recurring [Member] \| Obligations of State and Political Subdivisions [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	2,753,471	2,426,876
Fair Value, Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	3,259,449	1,472,280
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	365,120	489,316
Fair Value, Measurements, Recurring [Member] \| IRLCs [Member]
Activity in available-for-sale securities and other investments:
Asset Derivative Fair Value	1,279	4,618
Fair Value, Measurements, Recurring [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Activity in available-for-sale securities and other investments:
Loans held-for-sale	147
Liability Derivative Fair Value		(1,560)
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury securities [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	126,841
Fair Value, Measurements, Recurring [Member] \| Level 1 Inputs [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	131,271	4,557
Fair Value, Measurements, Recurring [Member] \| Level 1 Inputs [Member] \| U.S. Treasury securities [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	126,841
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	6,441,908	4,388,472
Loans held-for-sale	34,122	79,585
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Corporate Bonds [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	63,868
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Obligations of State and Political Subdivisions [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	2,753,471	2,426,876
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Residential Mortgage-Backed Securities [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	3,259,449	1,472,280
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Commercial Mortgage-Backed Securities [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	365,120	489,316
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| IRLCs [Member]
Activity in available-for-sale securities and other investments:
Asset Derivative Fair Value	1,279	4,618
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Activity in available-for-sale securities and other investments:
Loans held-for-sale	147
Liability Derivative Fair Value		(1,560)
Other Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	4,430	4,557
Other Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 Inputs [Member]
Activity in available-for-sale securities and other investments:
Securities available-for-sale, Estimated Fair Value	$ 4,430	$ 4,557

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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