Comprehensive Income - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 4,595,140	$ 4,718,628	$ 4,332,698	$ 4,297,620	$ 4,718,628	$ 4,297,620
Net current-period other comprehensive income, net of tax	(105,665)	(136,804)	8,662	(20,509)	(242,469)	(11,847)
Ending Balance	4,487,050	4,595,140	4,393,713	4,332,698	4,487,050	4,393,713
Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(29,841)			(29,841)
Other comprehensive income before reclassification					0
Amounts reclassified from accumulated other comprehensive income					1,281
Net current-period other comprehensive income, net of tax					1,281
Ending Balance	(28,560)				(28,560)
Unrealized Gains/Losses on AFS Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		8,594			8,594
Other comprehensive income before reclassification					(269,820)
Amounts reclassified from accumulated other comprehensive income					0
Net current-period other comprehensive income, net of tax					(269,820)
Ending Balance	(261,226)				(261,226)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(141,692)	(4,888)	1,861	22,370	(4,888)	22,370
Other comprehensive income before reclassification					(243,811)
Amounts reclassified from accumulated other comprehensive income					1,342
Net current-period other comprehensive income, net of tax	(105,665)	(136,804)	8,662	(20,509)	(242,469)
Ending Balance	(247,357)	(141,692)	$ 10,523	$ 1,861	(247,357)	$ 10,523
Unrealized Gains/Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		$ 16,359			16,359
Other comprehensive income before reclassification					26,009
Amounts reclassified from accumulated other comprehensive income					61
Net current-period other comprehensive income, net of tax					26,070
Ending Balance	$ 42,429				$ 42,429