Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 2,494	$ 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	55,536,916	54,055,600
VIE Current Assets Pledged	$ 23,700	$ 40,100
VIE Non-current Assets Pledged	435,400	423,300
VIE Current Liabilities, No Recourse	29,600	42,800
VIE Non-current Liabilities, No Recourse	$ 21,400	$ 14,700