Investments (Amortized Cost and Estimated Fair Values of Debt Securities Held-To-Maturity by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Amortized Cost
Due in one year or less	$ 846	$ 1,690
Due after one year through five years	13,098	6,763
Due after five years through ten years	170,411	163,252
Due after ten years	32,287	48,268
Total debt securities held-to-maturity	216,642	219,973
Estimated Fair Value
Due in one year or less	860	1,694
Due after one year through five years	13,656	6,938
Due after five years through ten years	173,352	164,787
Due after ten years	32,355	48,841
Total debt securities held-to-maturity	$ 220,223	$ 222,260