Common Stock and Preferred Stock (Details) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock, shares authorized	240,000,000	240,000,000
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000
Preferred stock, par value (in dollars per share)	$ 0.0001
Common stock, shares outstanding	68,196,964	69,326,202
Preferred stock, shares outstanding	0	0
Voting Common Stock
Class of Stock [Line Items]
Common stock, shares authorized	240,000,000
Common stock, par value (in dollars per share)	$ 0.0001
Non-Voting Common Stock
Class of Stock [Line Items]
Common stock, shares authorized	50,000,000
Common stock, par value (in dollars per share)	$ 0.0001
Common stock, shares outstanding	0	0