Accumulated Other Comprehensive Income (Loss) (Other Comprehensive Income (Loss) Reclassification Adjustments) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	$ 84,931	$ (65,235)
Reclassifications out of AOCI	(62)	729
Tax effect	(18,552)	14,078
Total other comprehensive income (loss), net of tax	66,317	(50,428)
Unrealized gains (losses) on debt securities
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	77,765	(61,483)
Reclassifications out of AOCI	41	569
Tax effect	(18,301)	14,118
Total other comprehensive income (loss), net of tax	59,505	(46,796)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	7,166	(3,752)
Reclassifications out of AOCI	0	0
Tax effect	(278)	0
Total other comprehensive income (loss), net of tax	6,888	(3,752)
Pension Benefit Adjustment
Accumulated Other Comprehensive Income Loss [Line Items]
Pretax change before reclassifications	0	0
Reclassifications out of AOCI	(103)	160
Tax effect	27	(40)
Total other comprehensive income (loss), net of tax	$ (76)	$ 120