Accumulated Other Comprehensive Income (Loss) (AOCI) (Components of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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)
Change in unrealized gains (losses) on debt securities				(77,058)
Change in foreign currency translation adjustment				(14,297)
Amortization of net actuarial loss				2,410
Amortization of prior service credit				(2,090)
Tax effect		$ 3,628	$ (9,127)	17,706	$ (25,496)
Accumulated other comprehensive income (loss) including non-controlling interest, Ending Balance		(181,368)		(181,368)
Allocated to the Company		(181,369)		(181,369)		$ (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
Cumulative-effect adjustment, net of taxes	[1]			(40,550)
Change in unrealized gains (losses) on debt securities				(77,058)
Tax effect		3,669	(6,874)	17,787	(21,055)
Accumulated other comprehensive income (loss) including non-controlling interest, Ending Balance		(63,018)		(63,018)
Allocated to the Company		(63,019)		(63,019)
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)
Change in foreign currency translation adjustment				(14,297)
Tax effect		0	0	0	0
Accumulated other comprehensive income (loss) including non-controlling interest, Ending Balance		(53,129)		(53,129)
Allocated to the Company		(53,129)		(53,129)
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)
Amortization of net actuarial loss				2,410
Amortization of prior service credit				(2,090)
Tax effect		(41)	$ (2,253)	(81)	$ (4,441)
Accumulated other comprehensive income (loss) including non-controlling interest, Ending Balance		(65,221)		(65,221)
Allocated to the Company		(65,221)		(65,221)
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	[1]			$ (40,550)

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