Comprehensive Income - Reclassifications Out 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
Available for sale ("AFS") securities:
Income before income taxes	$ 119,144		$ 119,291		$ 220,906	$ 253,754
Related income tax expense	(23,531)		(24,455)		(43,629)	(52,020)
Net income	95,613	$ 81,664	94,836	$ 106,898	177,277	201,734
Cash flow hedge:
Income before income taxes	119,144		119,291		220,906	253,754
Related income tax expense	(23,531)		(24,455)		(43,629)	(52,020)
Net income	95,613	81,664	94,836	106,898	177,277	201,734
Pension plan:
Amortization of net actuarial loss	832		1,589		1,656	3,161
Income before income taxes	119,144		119,291		220,906	253,754
Related income tax expense	(23,531)		(24,455)		(43,629)	(52,020)
Net income	$ 95,613	$ 81,664	$ 94,836	$ 106,898	177,277	$ 201,734
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains/Losses on AFS Securities [Member]
Available for sale ("AFS") securities:
Net reclassification adjustment for gains included in net income					0
Income before income taxes					0
Related income tax expense					0
Net income					0
Cash flow hedge:
Income before income taxes					0
Related income tax expense					0
Net income					0
Pension plan:
Income before income taxes					0
Related income tax expense					0
Net income					0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Available for sale ("AFS") securities:
Income before income taxes					(375)
Related income tax expense					1,281
Net income					1,342
Cash flow hedge:
Income before income taxes					(375)
Related income tax expense					1,281
Net income					1,342
Pension plan:
Net actuarial loss					1,656
Amortization of net actuarial loss					1,656
Income before income taxes					(375)
Related income tax expense					1,281
Net income					1,342
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain Loss Net Cash Flow Hedge Parent [Member]
Available for sale ("AFS") securities:
Income before income taxes					79
Related income tax expense					(18)
Net income					61
Cash flow hedge:
Net reclassification adjustment for losses					79
Income before income taxes					79
Related income tax expense					(18)
Net income					61
Pension plan:
Income before income taxes					79
Related income tax expense					(18)
Net income					$ 61