Debt Securities According Contractual Terms (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Debt And Receivables Securitization [Line Items]
Amortized costs, In one year or less	$ 74,930
Amortized costs, After one year through five years	163,686
Amortized costs, After five years through ten years	217,605
Amortized costs, After ten years	31,540
Amortized costs, Total	487,761
Fair Values, In one year or less	74,983
Fair Values, After one year through five years	170,006
Fair Values, After five years through ten years	231,292
Fair Values, After ten years	33,616
Debt securities, fair values total	$ 509,897