CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Accounts receivable, allowance for doubtful accounts	$ 13,358	$ 5,805
Stockholders' equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	200,000	200,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Treasury Stock, Shares	1,325,049	876,744
Consolidated VIEs [Member]
ASSETS
Consolidated VIEs, Assets	$ 426,879	$ 226,198
LIABILITIES AND STOCKHOLDERS' EQUITY
Consolidated VIEs, Liabilities	$ 81,832	$ 39,196
Class A Common Stock [Member]
Stockholders' equity:
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	47,291,463	31,621,369
Common stock, shares outstanding	45,966,414	30,744,625
Class B Common Stock [Member]
Stockholders' equity:
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	20,000,000	20,000,000
Common stock, shares issued	0	0
Common stock, shares outstanding	0	0
Class C Common Stock [Member]
Stockholders' equity:
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	5,000,000	5,000,000
Common stock, shares issued	0	0
Common stock, shares outstanding	0	0