Accumulated Other Comprehensive Income (Loss) (Other Comprehensive Income (Loss) Reclassification Adjustments) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	$ 25,602	$ 8,976	$ 110,241	$ 99,678
Reclassifications out of AOCI	152,373	(2,855)	150,627	4,298
Tax effect	(66,740)	(3,399)	(92,235)	(38,004)
Total other comprehensive income, net of tax	111,235	2,722	168,633	65,972
Unrealized Gains (Losses) on Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	22,833	12,435	95,329	96,612
Reclassifications out of AOCI	(928)	(8,687)	(14,285)	(13,222)
Tax effect	(7,976)	(1,169)	(29,030)	(31,303)
Total other comprehensive income, net of tax	13,929	2,579	52,014	52,087
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	11,415	(3,459)	23,558	3,066
Reclassifications out of AOCI	0	0	0	0
Tax effect	0	0	0	0
Total other comprehensive income, net of tax	11,415	(3,459)	23,558	3,066
Pension Benefit Adjustment
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	(8,646)	0	(8,646)	0
Reclassifications out of AOCI	153,301	5,832	164,912	17,520
Tax effect	(58,764)	(2,230)	(63,205)	(6,701)
Total other comprehensive income, net of tax	$ 85,891	$ 3,602	$ 93,061	$ 10,819