Employment Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employment Benefits [Abstract]
Employee contribution limit per calendar year for employees under 50 years of age	$ 19,000
Employee contribution limit per calendar year for employees over 50 years of age	25,000
Matching contributions	$ 6,400,000	$ 5,700,000	$ 3,000,000.0