Securities - Additional Information (Detail)		6 Months Ended
		Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) Investment	Dec. 31, 2015 USD ($) Investment
Schedule of Investments [Line Items]
Federal Home Loan Bank stock, at cost	[1]		$ 586,835,000	$ 663,971,000
Proceeds from sales of held to maturity securities		$ 19,730,000
Gross 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			$ 18,700,000	$ 24,900,000
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost			26.40%	2.00%
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost			$ 70,700,000	$ 1,200,000,000
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 | Investment				7
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			6	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 | Investment				2

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