Debt Securities According Contractual Terms (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Debt And Receivables Securitization [Line Items]
Amortized costs, In one year or less	$ 17,673
Amortized costs, After one year through five years	211,288
Amortized costs, After five years through ten years	208,966
Amortized costs, After ten years	32,286
Amortized costs, Total	470,213
Fair Values, In one year or less	17,905
Fair Values, After one year through five years	217,187
Fair Values, After five years through ten years	222,499
Fair Values, After ten years	34,595
Debt securities, fair values total	$ 492,186