Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Segment Entity Office Loan	Dec. 31, 2011 Entity
Schedule Of Significant Accounting Policies [Line Items]
Number of retail-banking offices	3
Number of non-performing loans	30
Amount of cash reserves with Federal Reserve Bank	$ 2.6
Number of active operating subsidiary	1	1
Number of reportable business segment	1
Maximum
Schedule Of Significant Accounting Policies [Line Items]
Cost method investment, ownership percentage in an affordable housing limited partnership	5.00%
Noncumulative preferred stock
Schedule Of Significant Accounting Policies [Line Items]
Preferred non-voting stock, par value	$ 0.01	0.01
Noncumulative preferred stock | Series A Preferred Stock
Schedule Of Significant Accounting Policies [Line Items]
Preferred non-voting stock, par value	$ 0.01
Preferred stock, liquidation preference per share	$ 10.00
Preferred stock dividend rates	5.00%
Noncumulative preferred stock | Series B Perpetual Preferred Stock
Schedule Of Significant Accounting Policies [Line Items]
Preferred non-voting stock, par value	$ 0.01
Preferred stock, liquidation preference per share	$ 10.00
Preferred stock dividend rates	5.00%
Noncumulative preferred stock | Series C Noncumulative Perpetual Convertible Preferred Stock
Schedule Of Significant Accounting Policies [Line Items]
Preferred non-voting stock, par value	$ 0.01
Preferred stock, liquidation preference per share	$ 13.00
Preferred stock conversion price	$ 13.00
Preferred stock dividend rates	5.00%
Cumulative Preferred Stock | Series D Fixed Rate Cumulative Perpetual Preferred Stock
Schedule Of Significant Accounting Policies [Line Items]
Preferred non-voting stock, par value	$ 0.01	0.01
Preferred stock, liquidation preference per share	$ 1,000.00
Cumulative Preferred Stock | Series D Fixed Rate Cumulative Perpetual Preferred Stock | First Five Years
Schedule Of Significant Accounting Policies [Line Items]
Preferred stock dividend rates	5.00%
Cumulative Preferred Stock | Series D Fixed Rate Cumulative Perpetual Preferred Stock | Thereafter
Schedule Of Significant Accounting Policies [Line Items]
Preferred stock dividend rates	9.00%
Cumulative Preferred Stock | Series E Fixed Rate Cumulative Perpetual Preferred Stock
Schedule Of Significant Accounting Policies [Line Items]
Preferred non-voting stock, par value	$ 0.01	0.01
Preferred stock, liquidation preference per share	$ 1,000.00
Cumulative Preferred Stock | Series E Fixed Rate Cumulative Perpetual Preferred Stock | First Five Years
Schedule Of Significant Accounting Policies [Line Items]
Preferred stock dividend rates	5.00%
Cumulative Preferred Stock | Series E Fixed Rate Cumulative Perpetual Preferred Stock | Thereafter
Schedule Of Significant Accounting Policies [Line Items]
Preferred stock dividend rates	9.00%
Buildings and related components | Minimum
Schedule Of Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives	10 years
Buildings and related components | Maximum
Schedule Of Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives	40 years
Furniture, fixtures and equipment | Minimum
Schedule Of Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives	3 years
Furniture, fixtures and equipment | Maximum
Schedule Of Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives	10 years
Leasehold Improvements
Schedule Of Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives description	amortized over the lease term or the estimated useful life of the asset whichever is shorter.