Debt and Equity Securities (Investments in Equity Securities, Classified as Available-For-Sale) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Equity securities, Amortized Cost	$ 325,734	$ 393,914
Equity securities, Gross unrealized gains	13,523	17,276
Equity securities, Gross unrealized losses	(17,972)	(8,778)
Equity securities	321,285	402,412
Preferred stocks
Schedule Of Available For Sale Securities [Line Items]
Equity securities, Amortized Cost	18,305	14,976
Equity securities, Gross unrealized gains	420	596
Equity securities, Gross unrealized losses	(3,258)	(47)
Equity securities	15,467	15,525
Common stocks
Schedule Of Available For Sale Securities [Line Items]
Equity securities, Amortized Cost	307,429	378,938
Equity securities, Gross unrealized gains	13,103	16,680
Equity securities, Gross unrealized losses	(14,714)	(8,731)
Equity securities	$ 305,818	$ 386,887