CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accumulated depreciation	$ 450,221	$ 374,738
Accumulated amortization	$ 64,064	$ 50,313
Voting units
Members' equity units, authorized (in units)	100	100
Members' equity units issued (in units)	100	100
Members' equity units outstanding (in units)	100	100
Non-voting units
Members' equity units, authorized (in units)	100	100
Members' equity units issued (in units)	100	100
Members' equity units outstanding (in units)	100	100