Stockholders' Equity - Stock Option Activity Under Equity-Based Plans (Details)	3 Months Ended
	Mar. 31, 2018 shares
Number of Shares
Balance (in shares)	1,296,863
Exercised (in shares)	(206,430)
Forfeited (in shares)	(4,167)
Balance (in shares)	1,086,266
Exercisable (in shares)	1,011,038