Investments (Securities Held to Maturity) (Details) - USD ($)
$ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
| Schedule of Held-to-maturity Securities [Line Items] |
|
|
| Totals |
$ 7,159,259
|
$ 7,173,967
|
| Gross Unrealized Gains |
220,495
|
247,892
|
| Gross Unrealized Losses |
(42,143)
|
(86,423)
|
| Fair Value |
7,337,611
|
7,335,436
|
| Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |
|
|
| Less than 12 Months, Fair Value |
1,580,333
|
1,986,981
|
| Less than 12 Months, Unrealized Losses |
(34,830)
|
(63,361)
|
| 12 Months or Greater, Fair Value |
188,056
|
445,573
|
| 12 Months or Greater, Unrealized Losses |
(7,313)
|
(23,062)
|
| Total, Fair Value |
1,768,389
|
2,432,554
|
| Gross Unrealized Losses |
(42,143)
|
(86,423)
|
| U.S. agencies |
|
|
| Schedule of Held-to-maturity Securities [Line Items] |
|
|
| Totals |
|
15,019
|
| Gross Unrealized Gains |
|
275
|
| Gross Unrealized Losses |
|
0
|
| Fair Value |
|
15,294
|
| Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |
|
|
| Gross Unrealized Losses |
|
0
|
| U.S. Treasury |
|
|
| Schedule of Held-to-maturity Securities [Line Items] |
|
|
| Totals |
1,333
|
1,927
|
| Gross Unrealized Gains |
235
|
317
|
| Gross Unrealized Losses |
0
|
0
|
| Fair Value |
1,568
|
2,244
|
| Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |
|
|
| Gross Unrealized Losses |
0
|
0
|
| States and political subdivisions |
|
|
| Schedule of Held-to-maturity Securities [Line Items] |
|
|
| Totals |
456,069
|
435,941
|
| Gross Unrealized Gains |
22,697
|
29,129
|
| Gross Unrealized Losses |
(2,841)
|
(662)
|
| Fair Value |
475,925
|
464,408
|
| Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |
|
|
| Less than 12 Months, Fair Value |
80,507
|
16,763
|
| Less than 12 Months, Unrealized Losses |
(2,841)
|
(387)
|
| 12 Months or Greater, Fair Value |
0
|
8,723
|
| 12 Months or Greater, Unrealized Losses |
0
|
(275)
|
| Total, Fair Value |
80,507
|
25,486
|
| Gross Unrealized Losses |
(2,841)
|
(662)
|
| Public utilities |
|
|
| Schedule of Held-to-maturity Securities [Line Items] |
|
|
| Totals |
1,087,176
|
1,044,063
|
| Gross Unrealized Gains |
36,904
|
42,271
|
| Gross Unrealized Losses |
(3,133)
|
(6,621)
|
| Fair Value |
1,120,947
|
1,079,713
|
| Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |
|
|
| Less than 12 Months, Fair Value |
162,587
|
298,962
|
| Less than 12 Months, Unrealized Losses |
(3,133)
|
(5,953)
|
| 12 Months or Greater, Fair Value |
0
|
17,840
|
| 12 Months or Greater, Unrealized Losses |
0
|
(668)
|
| Total, Fair Value |
162,587
|
316,802
|
| Gross Unrealized Losses |
(3,133)
|
(6,621)
|
| Corporate |
|
|
| Schedule of Held-to-maturity Securities [Line Items] |
|
|
| Totals |
4,237,029
|
4,160,628
|
| Gross Unrealized Gains |
116,720
|
114,920
|
| Gross Unrealized Losses |
(29,701)
|
(72,913)
|
| Fair Value |
4,324,048
|
4,202,635
|
| Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |
|
|
| Less than 12 Months, Fair Value |
1,063,194
|
1,522,544
|
| Less than 12 Months, Unrealized Losses |
(22,867)
|
(54,295)
|
| 12 Months or Greater, Fair Value |
179,113
|
323,567
|
| 12 Months or Greater, Unrealized Losses |
(6,834)
|
(18,618)
|
| Total, Fair Value |
1,242,307
|
1,846,111
|
| Gross Unrealized Losses |
(29,701)
|
(72,913)
|
| Residential mortgage-backed |
|
|
| Schedule of Held-to-maturity Securities [Line Items] |
|
|
| Totals |
1,367,270
|
1,503,021
|
| Gross Unrealized Gains |
42,345
|
59,013
|
| Gross Unrealized Losses |
(6,468)
|
(6,227)
|
| Fair Value |
1,403,147
|
1,555,807
|
| Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |
|
|
| Less than 12 Months, Fair Value |
274,045
|
148,712
|
| Less than 12 Months, Unrealized Losses |
(5,989)
|
(2,726)
|
| 12 Months or Greater, Fair Value |
8,943
|
95,443
|
| 12 Months or Greater, Unrealized Losses |
(479)
|
(3,501)
|
| Total, Fair Value |
282,988
|
244,155
|
| Gross Unrealized Losses |
(6,468)
|
(6,227)
|
| Home equity |
|
|
| Schedule of Held-to-maturity Securities [Line Items] |
|
|
| Totals |
8,826
|
11,047
|
| Gross Unrealized Gains |
1,462
|
1,701
|
| Gross Unrealized Losses |
0
|
0
|
| Fair Value |
10,288
|
12,748
|
| Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |
|
|
| Gross Unrealized Losses |
0
|
0
|
| Manufactured housing |
|
|
| Schedule of Held-to-maturity Securities [Line Items] |
|
|
| Totals |
1,556
|
2,321
|
| Gross Unrealized Gains |
132
|
266
|
| Gross Unrealized Losses |
0
|
0
|
| Fair Value |
1,688
|
2,587
|
| Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] |
|
|
| Gross Unrealized Losses |
$ 0
|
$ 0
|