CONSOLIDATED STATEMENTS OF CASH FLOWS (PARENTHETICAL) - USD ($) $ in Thousands |
3 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
Mar. 31, 2019 |
Mar. 31, 2018 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Statement of Cash Flows [Abstract] | |||||
| Interest capitalized | $ 23 | $ 474 | $ 1,179 | $ 2,137 | $ 524 |