Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Consolidated Balance Sheets
Receivables, allowance for doubtful accounts (in dollars)	$ 28	$ 12
Property and equipment, accumulated depreciation (in dollars)	723,320	678,988
Intangible assets, accumulated amortization (in dollars)	$ 14,020	$ 14,141
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	69,403,969	69,400,252
Common stock, shares outstanding	69,403,969	69,400,252