Securities - Additional Information (Detail)		9 Months Ended
		Sep. 30, 2015 USD ($) Investment	Dec. 31, 2014 USD ($) Investment
Schedule of Investments [Line Items]
Federal Home Loan Bank stock, at cost | $	[1]	$ 538,473,000	$ 515,327,000
Proceeds from sales of held to maturity securities | $		19,730,000
Gain realized gains from sales of held to maturity securities | $		543,000
Investment securities designated as having a continuous loss position for twelve months or more, unrealized losses | $		$ 21,900,000	$ 51,600,000
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost		1.70%	1.90%
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost | $		$ 1,300,000,000	$ 2,700,000,000
Minimum
Schedule of Investments [Line Items]
Percentage of amount collected to recognize sale of securities		85.00%
Agency Debt Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more		7	17
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
Mortgage-Related Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more		3	16
GSE CMOs
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more			3
Municipal bonds
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more			2
Preferred stock securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more			1

[1] Carrying value and estimated fair value are at cost.