Condensed consolidated balance sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts receivable, allowances	$ 661	$ 576
Borrowings under credit facilities, stated value	$ 1,086,978	$ 838,985
Class A common stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized shares	500,000,000	500,000,000
Common stock, issued shares	46,675,183	46,265,903
Common stock, outstanding shares	46,675,183	46,265,903
Class B common stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized shares	500,000,000	500,000,000
Common stock, issued shares	22,568,831	22,823,272
Common stock, outstanding shares	22,568,831	22,823,272