Other Comprehensive Income (Details) - USD ($)
$ in Thousands |
3 Months Ended |
9 Months Ended |
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward] |
|
|
|
|
| Accumulated other comprehensive loss at beginning of period |
|
|
$ 1,931,696
|
|
| Losses reclassified from net accumulated other comprehensive loss |
$ 26
|
$ 44
|
75
|
$ 129
|
| Accumulated other comprehensive loss at end of period |
2,025,733
|
|
2,025,733
|
|
| Gains and Losses on Cash Flow Hedges |
|
|
|
|
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward] |
|
|
|
|
| Accumulated other comprehensive loss at beginning of period |
(659)
|
(732)
|
(678)
|
(817)
|
| Other comprehensive income (loss) before reclassifications |
|
0
|
|
0
|
| Losses reclassified from net accumulated other comprehensive loss |
10
|
44
|
29
|
129
|
| Net current period other comprehensive income |
10
|
44
|
29
|
129
|
| Accumulated other comprehensive loss at end of period |
(649)
|
(688)
|
(649)
|
(688)
|
| Defined Benefit Pension and Postretirement Items |
|
|
|
|
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward] |
|
|
|
|
| Accumulated other comprehensive loss at beginning of period |
(582)
|
(441)
|
(612)
|
(464)
|
| Other comprehensive income (loss) before reclassifications |
|
12
|
|
35
|
| Losses reclassified from net accumulated other comprehensive loss |
16
|
0
|
46
|
0
|
| Net current period other comprehensive income |
16
|
12
|
46
|
35
|
| Accumulated other comprehensive loss at end of period |
(566)
|
(429)
|
(566)
|
(429)
|
| Total |
|
|
|
|
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward] |
|
|
|
|
| Accumulated other comprehensive loss at beginning of period |
(1,241)
|
(1,173)
|
(1,290)
|
(1,281)
|
| Other comprehensive income (loss) before reclassifications |
|
12
|
|
35
|
| Losses reclassified from net accumulated other comprehensive loss |
26
|
44
|
75
|
129
|
| Net current period other comprehensive income |
26
|
56
|
75
|
164
|
| Accumulated other comprehensive loss at end of period |
$ (1,215)
|
$ (1,117)
|
$ (1,215)
|
$ (1,117)
|