CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY - 9 months ended Sep. 30, 2018 $ in Thousands	USD ($) shares
Balance (in shares) at Dec. 31, 2017 | shares	933,000
Comprehensive income:
Net income | $	$ 77,613
Other comprehensive income | $	$ 69
Balance (in shares) at Sep. 30, 2018 | shares	933,000