CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 2,453	$ 1,523
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ 123,599	$ 105,133
Preferred stock, shares issued	0	0
Common Stock, Shares, To be Issued	100,000	100,000
Common Class A
Common stock, shares issued	58,432,677	52,798,303
Common stock, shares outstanding	58,432,677	52,798,303
Common Stock, Par or Stated Value Per Share	$ 0	$ 0
Common Class B
Common stock, shares issued	3,755	3,755
Common stock, shares outstanding	3,755	3,755
Common Stock, Par or Stated Value Per Share	$ 0	$ 0