Stockholders' Equity - Outstanding Options Granted to Consultants for Sales and Pre-marketing Services (Details)	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 0.000
Options exercisable at the end of the year (in shares)	548,421
Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options for shares of common stock (in shares)	23,493
Options exercisable at the end of the year (in shares)	22,836
February 2013 | Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options for shares of common stock (in shares)	1,500
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 12.470
Options exercisable at the end of the year (in shares)	1,500
Exercisable through	February 2023
August 2013 | Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options for shares of common stock (in shares)	4,000
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 21.140
Options exercisable at the end of the year (in shares)	4,000
Exercisable through	August 2023
March 2014 | Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options for shares of common stock (in shares)	5,550
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 39.860
Options exercisable at the end of the year (in shares)	5,550
Exercisable through	March 2024
May 2014 | Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options for shares of common stock (in shares)	3,700
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 22.010
Options exercisable at the end of the year (in shares)	3,700
Exercisable through	May 2024
November 2014 | Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options for shares of common stock (in shares)	5,468
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 21.660
Options exercisable at the end of the year (in shares)	5,468
Exercisable through	November 2024
May 2015 | Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options for shares of common stock (in shares)	1,137
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 19.510
Options exercisable at the end of the year (in shares)	1,055
Exercisable through	May 2025
February 2016 | Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options for shares of common stock (in shares)	2,138
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 16.870
Options exercisable at the end of the year (in shares)	1,563
Exercisable through	February 2026