Debt and Equity Securities (Investments in Equity Securities, Classified as Available-For-Sale) (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Equity securities, Amortized Cost	$ 326,190	$ 393,914
Equity securities, Gross unrealized gains	9,732	17,276
Equity securities, Gross unrealized losses	(23,887)	(8,778)
Equity securities	312,035	402,412
Preferred stocks
Schedule Of Available For Sale Securities [Line Items]
Equity securities, Amortized Cost	18,965	14,976
Equity securities, Gross unrealized gains	665	596
Equity securities, Gross unrealized losses	(3,985)	(47)
Equity securities	15,645	15,525
Common stocks
Schedule Of Available For Sale Securities [Line Items]
Equity securities, Amortized Cost	307,225	378,938
Equity securities, Gross unrealized gains	9,067	16,680
Equity securities, Gross unrealized losses	(19,902)	(8,731)
Equity securities	$ 296,390	$ 386,887