Investments (Amortized Cost and Estimated Fair Values of Debt Securities Held-To-Maturity by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Amortized Cost
Due in one year or less	$ 846	$ 1,690
Due after one year through five years	10,656	6,763
Due after five years through ten years	169,756	163,252
Due after ten years	35,608	48,268
Total debt securities held-to-maturity	216,866	219,973
Estimated Fair Value
Due in one year or less	865	1,694
Due after one year through five years	11,013	6,938
Due after five years through ten years	170,879	164,787
Due after ten years	35,123	48,841
Total debt securities held-to-maturity	$ 217,880	$ 222,260