Investments in debt and equity securities available-for-sale - Debt Securities According Contractual Terms (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]
Amortized costs, In one year or less	$ 1,610
Amortized costs, After one year through five years	262,946
Amortized costs, After five years through ten years	230,273
Amortized costs, After ten years	34,576
Amortized costs, Total	529,405
Fair Values, In one year or less	1,627
Fair Values, After one year through five years	268,276
Fair Values, After five years through ten years	236,883
Fair Values, After ten years	36,318
Debt securities, fair values total	$ 543,104