Employee Benefit Plans (Details)	12 Months Ended			192 Months Ended	216 Months Ended
	Dec. 31, 2017 USD ($) mo	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) yr age	Dec. 31, 2017 USD ($)
Employee Benefit Plans [Abstract]
Eligibility Period For 401K Savings Plan In Months | mo	3
Employer Matching Contribution, Percent of Match					200.00%
Employer Matching Contribution, Percent of Employees' Gross Pay					3.00%
Maximum Eligible Earnings As Established By IRS For Matching Contributions	$ 270,000	$ 265,000	$ 265,000
Employer Contribution Amount	4,100,000	4,000,000	3,700,000
Years Of Service For Supplemental Retirement Contribution | yr				10
Age Of Employee For Supplemental Retirement Contribution | age				40
Annual Supplemental Retirement Contribution And Credit Total.	18,000	21,000	$ 42,000
Separate Unrestricted Cash For Deferred Compensation Plan.	29,200,000	23,800,000		$ 23,800,000	$ 29,200,000
Deferred Compensation Liability	$ 29,200,000	$ 23,800,000		$ 23,800,000	$ 29,200,000