Debt and Equity Securities (Investments in Debt Securities, Classified as Available-For-Sale) (Detail) - USD ($)
$ in Thousands |
Jun. 30, 2016 |
Dec. 31, 2015 |
| Schedule Of Available For Sale Securities [Line Items] |
|
|
| Debt Securities, Amortized Cost |
$ 4,480,820
|
$ 4,290,864
|
| Debt Securities, Gross unrealized gains |
71,944
|
25,745
|
| Debt Securities, Gross unrealized losses |
(10,343)
|
(37,262)
|
| Debt securities, Estimated fair value |
4,542,421
|
4,279,347
|
| U.S. Treasury Bonds |
|
|
| Schedule Of Available For Sale Securities [Line Items] |
|
|
| Debt Securities, Amortized Cost |
121,611
|
130,252
|
| Debt Securities, Gross unrealized gains |
2,777
|
421
|
| Debt Securities, Gross unrealized losses |
|
(1,301)
|
| Debt securities, Estimated fair value |
124,388
|
129,372
|
| Municipal Bonds |
|
|
| Schedule Of Available For Sale Securities [Line Items] |
|
|
| Debt Securities, Amortized Cost |
743,942
|
692,000
|
| Debt Securities, Gross unrealized gains |
23,407
|
12,640
|
| Debt Securities, Gross unrealized losses |
(434)
|
(845)
|
| Debt securities, Estimated fair value |
766,915
|
703,795
|
| Foreign Government Bonds |
|
|
| Schedule Of Available For Sale Securities [Line Items] |
|
|
| Debt Securities, Amortized Cost |
141,315
|
129,984
|
| Debt Securities, Gross unrealized gains |
2,058
|
1,132
|
| Debt Securities, Gross unrealized losses |
(56)
|
(1,015)
|
| Debt securities, Estimated fair value |
143,317
|
130,101
|
| Governmental Agency Bonds |
|
|
| Schedule Of Available For Sale Securities [Line Items] |
|
|
| Debt Securities, Amortized Cost |
338,201
|
419,869
|
| Debt Securities, Gross unrealized gains |
3,554
|
1,023
|
| Debt Securities, Gross unrealized losses |
|
(2,801)
|
| Debt securities, Estimated fair value |
341,755
|
418,091
|
| Governmental Agency Mortgage-Backed Securities |
|
|
| Schedule Of Available For Sale Securities [Line Items] |
|
|
| Debt Securities, Amortized Cost |
2,207,589
|
2,065,728
|
| Debt Securities, Gross unrealized gains |
15,830
|
4,984
|
| Debt Securities, Gross unrealized losses |
(5,607)
|
(15,039)
|
| Debt securities, Estimated fair value |
2,217,812
|
2,055,673
|
| U.S. Corporate Debt Securities |
|
|
| Schedule Of Available For Sale Securities [Line Items] |
|
|
| Debt Securities, Amortized Cost |
701,935
|
642,869
|
| Debt Securities, Gross unrealized gains |
19,582
|
4,297
|
| Debt Securities, Gross unrealized losses |
(3,135)
|
(12,483)
|
| Debt securities, Estimated fair value |
718,382
|
634,683
|
| Foreign Corporate Debt Securities |
|
|
| Schedule Of Available For Sale Securities [Line Items] |
|
|
| Debt Securities, Amortized Cost |
226,227
|
210,162
|
| Debt Securities, Gross unrealized gains |
4,736
|
1,248
|
| Debt Securities, Gross unrealized losses |
(1,111)
|
(3,778)
|
| Debt securities, Estimated fair value |
$ 229,852
|
$ 207,632
|