Noninterest Income - Gains and Losses on Investments (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Gains and Losses on Investments [Abstract]
Total net gains on non-marketable and other equity securities	$ 36,114	$ 17,753	$ 45,172	$ 33,115
Marketable Securities, Realized Gain (Loss)	0	(123)	0	485
Gains on investment securities, net	$ 36,114	$ 17,630	$ 45,172	$ 33,600

- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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