Regulatory Decision and Related Accounting and Policy Changes - Summary of Collective Revenue Requirement Phased-in Over Time (Details) $ in Thousands	Sep. 30, 2016 USD ($)
Regulated Operations [Abstract]
2015, Incremental revenue requirement	$ 1,083
2016, Incremental revenue requirement	887
2017, Incremental revenue requirement	335
2018, Incremental revenue requirement	335
2019, Incremental revenue requirement	335
2020, Incremental revenue requirement	335
2021, Incremental revenue requirement	335
2015, Cumulative revenue requirement	1,083
2016, Cumulative revenue requirement	1,970
2017, Cumulative revenue requirement	2,305
2018, Cumulative revenue requirement	2,640
2019, Cumulative revenue requirement	2,975
2020, Cumulative revenue requirement	3,310
2021, Cumulative revenue requirement	$ 3,645