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Securities - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Investment	Dec. 31, 2017 USD ($) Investment	Dec. 31, 2016 USD ($)
Schedule of Investments [Line Items]
Federal Home Loan Bank stock, at cost	$ 644,590	$ 603,819
Amortized cost from sales of held to maturity securities		521,000
Proceeds from sales of held to maturity securities		547,925	$ 1,297
Gross realized gains from sales of held to maturity securities		26,900
Securities transferred from held to maturity to available for sale		3,040,305
Unrealized gain on securities transferred from held to maturity to available for sale		82,800
Investment securities designated as having a continuous loss position for twelve months or more, unrealized losses	$ 22,500	$ 10,100
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost	2.90%	8.50%
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost	$ 782,400	$ 118,200
Capital trust notes
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more | Investment	5	5
Municipal bonds
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more | Investment	3	2
Mutual Fund
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more | Investment	1	1

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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