Six Months Ended | Years Ended December 31, | |||||||||||||||||||||||
| June 30, 2018 | 2017 | 2016 | 2015 | 2014 | 2013 | |||||||||||||||||||
| Income from continuing operations before income taxes | $ | 116,400 | $ | 240,023 | $ | 352,031 | $ | 218,289 | $ | 339,347 | $ | 254,194 | ||||||||||||
| Distributions greater than equity in earnings of affiliates | — | — | — | — | — | — | ||||||||||||||||||
| Previously capitalized interest charged to earnings during the period | 82 | 54 | — | — | — | — | ||||||||||||||||||
| Interest and expense on indebtedness, excluding capitalized interest | 27,693 | 50,428 | 40,041 | 33,531 | 36,646 | 14,608 | ||||||||||||||||||
| Interest portion of rentals * | 2,665 | 4,737 | 7,728 | 7,473 | 2,842 | 2,380 | ||||||||||||||||||
| Earnings before provision for taxes and fixed charges | $ | 146,840 | 295,242 | 399,800 | 259,293 | 378,835 | 271,182 | |||||||||||||||||
| Interest and expense on indebtedness, excluding capitalized interest | $ | 27,693 | $ | 50,428 | $ | 40,041 | $ | 33,531 | $ | 36,646 | $ | 14,608 | ||||||||||||
| Capitalized interest | (1,331 | ) | (3,768 | ) | (337 | ) | — | — | — | |||||||||||||||
| Interest portion of rentals* | 2,665 | 4,737 | 7,728 | 7,473 | 2,842 | 2,380 | ||||||||||||||||||
| Total fixed charges | $ | 29,027 | 51,397 | 47,432 | 41,004 | 39,488 | 16,988 | |||||||||||||||||
| Ratio of earnings to fixed charges | 5.1 | 5.7 | 8.4 | 6.3 | 9.6 | 16.0 | ||||||||||||||||||
