Stockholders' Equity - Weighted Average Assumptions of Fair Value Options Using Black-Scholes Option-Pricing Model (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate, minimum	2.50%	1.70%	1.00%
Risk-free interest rate, maximum	3.10%	2.10%	1.80%
Expected life (in years)	5 years	5 years	5 years
Historical volatility, minimum	43.50%	46.60%	46.80%
Historical volatility, maximum	48.40%	48.10%	48.20%