Investment Securities - Changes to Carrying Amount of Other Investments without Readily Determinable Fair Value (Detail) $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($)
Investments, Debt and Equity Securities [Abstract]
Carrying value as of January 1, 2018	$ 27,680
Upward carrying value adjustments	3,630
Downward carrying value adjustments	(1,611)
Additions	3,654
Sales and dispositions	(9,338)
Carrying value as of June 30, 2018	$ 24,015

Equity Securities Without Readily Determinable Fair Value, Additions, Annual Amount

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Amount of investment in equity security without readily determinable fair value.

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Amount of loss from downward price adjustment on investment in equity security without readily determinable fair value.

No definition available.

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Equity Securities Without Readily Determinable Fair Value, Sales And Dispositions, Annual Amount

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Amount of gain from upward price adjustment on investment in equity security without readily determinable fair value.

No definition available.

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