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Changes in Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss), tax	$ (92)	$ (451)	$ (445)
Reclassification of income tax effects from the Tax Reform Act, net of tax	769
Reclassification of unrealized gains on equity securities, net of tax	21	297	255
Foreign currency translation adjustments, tax	0	0	0
Unrealized (losses) gains on marketable securities, tax	(521)	1,815	209
Retirement plans prior service benefit, tax	(1,081)	(932)	(778)
Foreign Currency Translation Reclassification Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, tax	0	0
Amounts reclassified from accumulated other comprehensive income (loss), tax	0	0
Other comprehensive income (loss), tax	0	0
Reclassification of income tax effects from the Tax Reform Act, net of tax	0
Unrealized (Losses) Gains on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, tax	(722)	1,903
Amounts reclassified from accumulated other comprehensive income (loss), tax	(21)	(297)	(255)
Other comprehensive income (loss), tax	(743)	1,606
Reclassification of income tax effects from the Tax Reform Act, net of tax	(691)
Reclassification of unrealized gains on equity securities, net of tax	902
Amortization of Prior Service Credit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, tax	0	0
Amounts reclassified from accumulated other comprehensive income (loss), tax	(71)	(154)	$ (190)
Other comprehensive income (loss), tax	(71)	$ (154)
Reclassification of income tax effects from the Tax Reform Act, net of tax	(78)
ASU 2016-01 | Foreign Currency Translation Reclassification Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification of unrealized gains on equity securities, net of tax	0
ASU 2016-01 | Unrealized (Losses) Gains on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification of unrealized gains on equity securities, net of tax	(902)
ASU 2016-01 | Amortization of Prior Service Credit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification of unrealized gains on equity securities, net of tax	$ 0

X

- Definition

The tax effect from accumulated appreciation or loss, in value of the total of unsold securities at the end of an accounting period.

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The tax effect from the total of net (gain) loss, prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

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The tax effect from accumulated adjustment, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains (losses).

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Amount of tax expense (benefit) allocated to other comprehensive income (loss) before reclassification adjustment from accumulated other comprehensive income (loss).

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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