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Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Net income | $ 107,251 | $ 87,351 | $ 193,490 | $ 165,891
Other comprehensive income: |  |  |  |
Reclassification adjustment for loss on derivative instruments included in net income, net of tax of $55 and $56 for the three months ended and $164 and $168 for the nine months ended in 2018 and 2017, respectively | 92 | 92 | 279 | 275
Postretirement liability adjustment: |  |  |  |
Amortization of postretirement liability losses included in net periodic benefit cost (credit), net of tax of $142 and $203 for the three months ended and $442 and $609 for the nine months ended in 2018 and 2017, respectively | 442 | 333 | 1,309 | 1,002
Reclassification of postretirement liability adjustment from regulatory asset, net of tax of $0 and $0 for the three months ended and $0 and $(725) for the nine months ended in 2018 and 2017, respectively | 0 | 0 | 0 | (917)
Postretirement liability adjustment | 442 | 333 | 1,309 | 85
Foreign currency translation adjustment: |  |  |  |
Foreign currency translation adjustment recognized during the period, net of tax of $0 and $9 for the three months ended and $(14) and $5 for the nine months ended in 2018 and 2017, respectively | 0 | 15 | (61) | 9
Reclassification adjustment for foreign currency translation adjustment included in net income, net of tax of $0 and $0 for the three months ended and $75 and $0 for the nine months ended in 2018 and 2017, respectively | 0 | 0 | 249 | 0
Foreign currency translation adjustment | 0 | 15 | 188 | 9
Net unrealized gain (loss) on available-for-sale investments: |  |  |  |
Net unrealized loss on available-for-sale investments arising during the period, net of tax of $(13) and $(10) for the three months ended and $(52) and $(38) for the nine months ended in 2018 and 2017, respectively | (51) | (19) | (199) | (70)
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax of $9 and $14 for the three months ended and $26 and $50 for the nine months ended in 2018 and 2017, respectively | 33 | 27 | 97 | 93
Net unrealized gain (loss) on available-for-sale investments | (18) | 8 | (102) | 23
Other comprehensive income | 516 | 448 | 1,674 | 392
Comprehensive income attributable to common stockholders | $ 107,767 | $ 87,799 | $ 195,164 | $ 166,283

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