XML 91 R77.htm IDEA: XBRL DOCUMENT v3.7.0.1
COMMITMENTS AND CONTINGENCIES - Coal Purchase Requirements (Details) - Coal
$ in Thousands
Dec. 31, 2016
USD ($)
Annual minimum coal purchases under contracts  
2017 $ 105,457
2018 103,389
2019 104,686
2020 82,612
2021 61,538
Thereafter 2,654
Total obligation $ 460,336