Investment Securities (Summary of Unrealized Losses) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months Fair Value	$ 130,703	$ 20
Less than 12 months Unrealized Losses	(320)	(1)
12 months or more, Fair Value	8
12 months or more, Unrealized Losses	(1)
Total, Fair Value	130,711	20
Total Unrealized losses	(321)	(1)
Residential Mortgage Pass-Through Securities Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months Fair Value	17	20
Less than 12 months Unrealized Losses		(1)
12 months or more, Fair Value	8
12 months or more, Unrealized Losses	(1)
Total, Fair Value	25	20
Total Unrealized losses	(1)	(1)
Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months Fair Value	130,686
Less than 12 months Unrealized Losses	(320)
12 months or more, Fair Value
12 months or more, Unrealized Losses
Total, Fair Value	130,686
Total Unrealized losses	$ (320)