Investments (Amortized Cost and Estimated Fair Values of Debt Securities Held-To-Maturity by Contractual Maturity) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Amortized Cost
Due in one year or less	$ 1,690,000	$ 1,720,000
Due after one year through five years	6,763,000	3,249,000
Due after five years through ten years	163,252,000	139,033,000
Due after ten years	48,268,000	80,636,000
Total debt securities held-to-maturity	219,973,000	224,638,000
Estimated Fair Value
Due in one year or less	1,694,000	1,725,000
Due after one year through five years	6,938,000	3,269,000
Due after five years through ten years	164,787,000	135,074,000
Due after ten years	48,841,000	75,939,000
Total debt securities held-to-maturity	$ 222,260,000	$ 216,007,000