Stockholders Equity (Tables)

6 Months Ended

Jun. 30, 2018

Class A Common Stock

Class Of Stock [Line Items]

Schedule of Shares Offered and Increase in Shares Outstanding in Follow-on Offerings

	Total Shares		Total Increase in
Date of Offering	Offered		Shares Outstanding
November, 2014		6,325,000		4,511,058
January, 2017		5,750,000		5,356,876
July, 2017		6,000,000		5,680,903
March, 2018		5,000,000		4,689,295
Total		23,075,000		20,238,132

Class B Common Stock

Class Of Stock [Line Items]

Schedule of Shares Offered and Increase in Shares Outstanding in Follow-on Offerings

	Class  B Stock
	Purchased /			Purchase Cost
Date of Offering	Surrendered			(in thousands)
November, 2014		4,507,453	$		28
January, 2017		5,356,876			101
July, 2017		5,680,903			128
March, 2018		4,689,295			135
Total		20,234,527	$		392