Business Combinations Business Combinations - Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands |
Dec. 31, 2016 |
Feb. 01, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|---|---|---|---|---|
| Business Acquisition [Line Items] | ||||
| Goodwill | $ 70,550 | $ 63,288 | $ 63,288 | |
| Santa Buckley Energy, Inc. (SBE) | ||||
| Business Acquisition [Line Items] | ||||
| Derivative assets | $ 22,678 | |||
| Other current assets and prepaids | 2,168 | |||
| Intangibles and other | 6,539 | |||
| Natural gas transportation assets | 8,040 | |||
| Total identifiable assets acquired | 39,425 | |||
| Accrued liabilities | (219) | |||
| Derivative liabilities | (15,007) | |||
| Natural gas transportation liabilities | (2,396) | |||
| Total liabilities assumed | (17,622) | |||
| Net identifiable assets acquired | 21,803 | |||
| Goodwill | 7,262 | |||
| Net assets acquired | $ 29,065 |