Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 2,531	$ 2,531
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.20	$ 0.20
Common stock, shares authorized	175,000,000	175,000,000
Common stock, shares issued	55,467,987	54,055,600
VIE Current Assets Pledged	$ 28,900	$ 40,100
VIE Non-current Assets Pledged	428,100	423,300
VIE Current Liabilities, No Recourse	36,000	42,800
VIE Non-current Liabilities, No Recourse	$ 14,000	$ 14,700