Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 2,531	$ 2,450
Preferred stock, par value	$ 1	$ 1
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, issued	0	0
Common stock, par value	$ 0.2	$ 0.2
Common stock, shares authorized	175,000,000	175,000,000
Common stock, shares issued	54,055,600	52,880,134
Other Comprehensive Income (Loss), Tax	$ (155)	$ 39
VIE Current assets pledged	41,700
VIE Non-current assets pledged	421,600
VIE Current liabilities, no recourse	42,800
VIE Non-current liabilities, no recourse	$ 14,700