Securities - Additional Information (Detail) $ in Thousands	Jun. 30, 2019 USD ($) Investment age	Dec. 31, 2018 USD ($) Investment
Schedule of Investments [Line Items]
Federal Home Loan Bank stock, at cost | $	$ 582,348	$ 644,590
Investment securities designated as having a continuous loss position for twelve months or more, unrealized losses | $	$ 7,800	$ 22,500
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost	1.50%	2.90%
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost | $	$ 528,200	$ 782,400
Mortgage-related Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more	7	9
Capital trust notes
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more	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	3	3
Mutual Fund
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more	1	1
US Government agencies securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more	4	9
Collateralized mortgage obligations
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more		7