CONSOLIDATED BALANCE SHEETS (Parenthetical - unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, net of allowance for doubtful accounts (in dollars)	$ 27,582	$ 25,345
Other accounts receivable, net of allowance for doubtful accounts (in dollars)	283	268
Accumulated depreciation	$ 67,077	$ 67,202
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	33,803,736	33,406,364
Common stock, shares outstanding	33,803,736	33,406,364