Investment Securities Held-to-Maturity - Unrealized Market Loss of Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	$ 135,345	$ 18,930
Less Than 12 Months, Unrealized Losses	1,173	58
12 Months or Longer, Fair Value	5,015	5,371
12 Months or Longer, Unrealized Losses	139	24
Total, Fair Value	140,360	24,301
Total, Unrealized Losses	1,312	82
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	9,670	9,994
Less Than 12 Months, Unrealized Losses	330	8
Total, Fair Value	9,670	9,994
Total, Unrealized Losses	330	8
U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	125,675	8,936
Less Than 12 Months, Unrealized Losses	843	50
12 Months or Longer, Fair Value	5,015	5,371
12 Months or Longer, Unrealized Losses	139	24
Total, Fair Value	130,690	14,307
Total, Unrealized Losses	$ 982	$ 74