Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accounts receivable, credit loss reserve	$ 4,839	$ 3,217
Accumulated depreciation	$ 1,540,249	$ 1,510,117
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	119,629,000	119,096,000
Common stock, shares outstanding	119,629,000	119,096,000