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Acquisitions (Narrative) (Details) - USD ($) $ in Thousands |  |  |  | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Feb. 13, 2020 | Jan. 15, 2020 | Aug. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Goodwill |  |  |  | $ 378,740 |  | $ 378,740 |  | $ 329,705
Total acquisition-related costs |  |  |  | 1,222 | $ 4 | 2,482 | $ 4 |
Delta Separations |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Aggregate consideration for acquisition | $ 47,100 |  |  |  |  |  |  |
Goodwill | $ 32,906 |  |  |  |  |  |  |
Thermo Energy Systems |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Aggregate consideration for acquisition |  | $ 7,300 |  |  |  |  |  |
Goodwill |  | $ 16,062 |  |  |  |  |  |
Apeks |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Aggregate consideration for acquisition |  |  | $ 12,600 |  |  |  |  |
Goodwill |  |  | $ 6,436 |  |  |  |  |
Selling, general and administrative costs |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Total acquisition-related costs |  |  |  | $ 588 | $ 4 | $ 1,848 | $ 4 |

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