Accumulated Other Comprehensive Income (Loss) (AOCI) (Components of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss) including non-controlling interest, Beginning Balance			$ (67,489)		$ (67,489)
Change in unrealized gains (losses) on debt securities					(96,416)
Change in foreign currency translation adjustment					(11,856)
Amortization of net actuarial loss					3,615
Amortization of prior service credit					(3,135)
Tax effect		$ 5,213		$ (66,740)	22,920		$ (92,235)
Accumulated other comprehensive income (loss) including non-controlling interest, Ending Balance		(192,911)			(192,911)
Allocated to the Company		(192,912)			(192,912)			$ (67,509)
Allocated to noncontrolling interests		1			1
Unrealized Gains (Losses) on Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss) including non-controlling interest, Beginning Balance			36,803		36,803
Cumulative-effect adjustment, net of taxes	[1]				(40,550)
Change in unrealized gains (losses) on debt securities					(96,416)
Tax effect		4,695		(7,976)	22,483		(29,030)
Accumulated other comprehensive income (loss) including non-controlling interest, Ending Balance		(77,680)			(77,680)
Allocated to the Company		(77,681)			(77,681)
Allocated to noncontrolling interests		1			1
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss) including non-controlling interest, Beginning Balance			(38,832)		(38,832)
Change in foreign currency translation adjustment					(11,856)
Tax effect		560		0	560		0
Accumulated other comprehensive income (loss) including non-controlling interest, Ending Balance		(50,128)			(50,128)
Allocated to the Company		(50,128)			(50,128)
Allocated to noncontrolling interests		0			0
Pension Benefit Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss) including non-controlling interest, Beginning Balance			(65,460)		(65,460)
Amortization of net actuarial loss					3,615
Amortization of prior service credit					(3,135)
Tax effect		(42)		$ (58,764)	(123)		$ (63,205)
Accumulated other comprehensive income (loss) including non-controlling interest, Ending Balance		(65,103)			(65,103)
Allocated to the Company		(65,103)			(65,103)
Allocated to noncontrolling interests		$ 0			0
Accumulated Other Comprehensive Loss | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative-effect adjustment, net of taxes			$ (40,550)		$ (40,550)	[1]

[1] The Company recognized a cumulative-effect adjustment to retained earnings for cumulative net unrealized gains related to its investments in equity securities upon adoption of new accounting guidance on January 1, 2018. See Note 1 Basis of Condensed Consolidated Financial Statements for further discussion of the new guidance.