Debt and Equity Securities (Investments in Equity Securities, Classified as Available-For-Sale) (Detail) - USD ($) $ in Thousands |
Mar. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Schedule Of Available For Sale Securities [Line Items] | ||
| Equity securities, Amortized Cost | $ 394,719 | $ 325,734 |
| Equity securities, Gross unrealized gains | 19,163 | 13,523 |
| Equity securities, Gross unrealized losses | (17,245) | (17,972) |
| Equity securities | 396,637 | 321,285 |
| Preferred stocks | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Equity securities, Amortized Cost | 19,657 | 18,305 |
| Equity securities, Gross unrealized gains | 385 | 420 |
| Equity securities, Gross unrealized losses | (4,596) | (3,258) |
| Equity securities | 15,446 | 15,467 |
| Common stocks | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Equity securities, Amortized Cost | 375,062 | 307,429 |
| Equity securities, Gross unrealized gains | 18,778 | 13,103 |
| Equity securities, Gross unrealized losses | (12,649) | (14,714) |
| Equity securities | $ 381,191 | $ 305,818 |