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STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Gross Margin |  |  |  |
Revenues from contracts with customers | $ 291,168 | $ 274,033 | $ 926,405 | $ 810,193
Other revenue | 1,353 | 5,656 | 4,580 | 19,904
Regulated Operating Revenue | 292,521 | 279,689 | 930,985 | 830,097
Cost of natural gas | 94,159 | 82,572 | 444,578 | 345,726
Net margin | 198,362 | 197,117 | 486,407 | 484,371
Operating expenses |  |  |  |
Operations and maintenance | 102,995 | 96,928 | 205,660 | 201,972
Depreciation and amortization | 39,757 | 37,851 | 78,647 | 74,870
General taxes | 14,567 | 13,973 | 30,767 | 29,719
Total operating expenses | 157,319 | 148,752 | 315,074 | 306,561
Operating income | 41,043 | 48,365 | 171,333 | 177,810
Other expense, net | (2,194) | (3,900) | (4,358) | (7,307)
Interest expense, net | (12,003) | (11,305) | (24,355) | (22,786)
Income before income taxes | 26,846 | 33,160 | 142,620 | 147,717
Income taxes | (6,427) | (12,537) | (31,366) | (50,638)
Net income | $ 20,419 | $ 20,623 | $ 111,254 | $ 97,079
Earnings per share |  |  |  |
Basic | $ 0.39 | $ 0.39 | $ 2.11 | $ 1.85
Diluted | $ 0.39 | $ 0.39 | $ 2.10 | $ 1.83
Average shares (thousands) |  |  |  |
Basic | 52,692 | 52,553 | 52,648 | 52,565
Diluted | 52,899 | 52,969 | 52,898 | 53,012
Dividends declared per share of stock | $ 0.46 | $ 0.42 | $ 0.92 | $ 0.84

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