Accumulated Other Comprehensive Income (Loss) (Other Comprehensive Income (Loss) Reclassification Adjustments) (Detail) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	$ (62,918)			$ 19,927			$ (124,823)	$ 92,894
Reclassifications out of AOCI	(5,561)			(6,083)			(13,725)	(3,545)
Tax effect	14,148			(1,387)			32,865	(24,044)
Total other comprehensive (loss) income, net of tax	(54,331)	$ 44,018	$ (95,370)	12,457	$ 73,301	$ (20,453)	(105,683)	65,305
Unrealized Gains (Losses) on Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	(49,970)			9,110			(120,979)	102,392
Reclassifications out of AOCI	(6,925)			(6,627)			(17,817)	(5,175)
Tax effect	14,181			(499)			33,942	(24,000)
Total other comprehensive (loss) income, net of tax	(42,714)			1,984			(104,854)	73,217
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	(12,948)			10,817			(3,844)	(9,498)
Reclassifications out of AOCI	0			0			0	0
Tax effect	329			(743)			9	389
Total other comprehensive (loss) income, net of tax	(12,619)			10,074			(3,835)	(9,109)
Pension Benefit Adjustment
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	0			0			0	0
Reclassifications out of AOCI	1,364			544			4,092	1,630
Tax effect	(362)			(145)			(1,086)	(433)
Total other comprehensive (loss) income, net of tax	$ 1,002			$ 399			$ 3,006	$ 1,197