Employee Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Definedcontributionemployeeautomaticcontributionpercentag	6.00%
Employer matching contributions	$ 8,100,000	$ 6,100,000	$ 5,900,000
Administrative expenses	$ 0	0	40,000
Profits sharing, percent of pre-tax profit paid to eligible employees on quarterly basis	10.00%
Profit sharing expense	$ 6,200,000	$ 8,400,000	$ 9,000,000
Effective January 1, 2016
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match	175.00%
Maximum annual contributions per employee, percent	6.00%