Stockholders' Equity - Weighted Average Assumptions Stock Options Granted (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Expected life from date of grant (years)	5 years 3 months 18 days	5 years 3 months 18 days	5 years 3 months 18 days
Expected volatility	33.20%	34.30%	36.20%
Risk-free interest rate	1.31%	2.46%	2.50%