Employee Benefit Plans - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2007
Retirement Benefits [Abstract]
Eligibility period for 401K savings plan, period	3 months
401(k) plan, maximum participant deferral percent	60.00%
401(k) plan, employer match per dollar of participant contribution	$ 0.50
401(k) plan, maximum employer match percentage	10.00%
401(k) plan, contributions made	$ 1,500,000	$ 1,300,000	$ 1,200,000
Deferred Compensation, maximum participant deferral percent				70.00%
Deferred Compensation, maximum director fees and bonuses that may be deferred (percent)				100.00%
Deferred Compensation, mandatory Company contributions as percentage of gross monthly salary (percent)				10.00%
Deferred Compensation, liability under Plan	$ 21,700,000	$ 20,600,000