Investments in debt and equity securities available-for-sale - Debt Securities According to Contractual Terms (Detail) $ in Thousands	Jun. 30, 2015 USD ($)
Investments, Debt and Equity Securities [Abstract]
Amortized costs, In one year or less	$ 44,224
Amortized costs, After one year through five years	226,379
Amortized costs, After five years through ten years	213,073
Amortized costs, After ten years	38,303
Amortized costs, Total	521,979
Fair Values, In one year or less	44,589
Fair Values, After one year through five years	232,501
Fair Values, After five years through ten years	218,150
Fair Values, After ten years	39,279
Debt securities, fair values total	$ 534,519