Securities - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Schedule of Investments [Line Items]
Available for Sale, fair value	$ 315,090,000	[1]	$ 429,266,000	[2]
Federal Home Loan Bank stock, at cost	482,173,000		469,145,000
Proceeds from sales of held to maturity securities	191,142,000
Gain realized gains from sales of held to maturity securities	11,600,000
Commitments to purchase securities	413,100,000
Investment securities designated as having a continuous loss position for twelve months or more, unrealized losses	14,600,000		21,100,000
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost	26.20%		24.50%
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost	55,400,000		86,100,000
Capital trust notes
Schedule of Investments [Line Items]
Number of pooled trust preferred securities	3
Pooled trust preferred securities with no excess subordination	2
Pooled trust preferred securities with excess subordination	1
Pooled trust preferred securities, excess subordination percentage	22.00%
Number of investment securities designated as having a continuous loss position for twelve months or more	6		7
Capital trust notes | Trust Preferred Securities
Schedule of Investments [Line Items]
Fair value	99,500,000
Mortgage-Related Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more	2		1
Equity Securities
Schedule of Investments [Line Items]
Number of investment securities designated as having a continuous loss position for twelve months or more	3		3
Minimum
Schedule of Investments [Line Items]
Percentage of amount collected to recognize sale of securities	85.00%
Other Securities
Schedule of Investments [Line Items]
Available for Sale, fair value	209,201,000		252,011,000
Other Securities | Common stock
Schedule of Investments [Line Items]
Available for Sale, fair value	51,649,000		42,262,000
Other Securities | Corporate preferred stock
Schedule of Investments [Line Items]
Available for Sale, fair value	$ 121,700,000

[1] At June 30, 2013, the non-credit portion of OTTI recorded in accumulated other comprehensive loss ("AOCL") was $570,000 (before taxes).

[2] At December 31, 2012, the non-credit portion of OTTI recorded in AOCL was $570,000 (before taxes).