Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Treasury stock, shares	4,223,670	1,861,089
Voting Common Stock
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	240,000,000	240,000,000
Common stock, shares issued	73,549,872	73,402,877
Common stock, shares outstanding	69,326,202	71,541,788