Employee Benefit Plans (Details Textual)	12 Months Ended
	Dec. 31, 2018 USD ($) quarter hour year	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
401(k) and Profit Sharing Plan
401(k) and Profit Sharing Plans
Minimum age required to be considered eligible for plan | year	21
Period of Employment Required to be Eligible for Plan	3 months
Minimum number of quarters required to be eligible for employer discretionary contribution | quarter	1
Minimum number of hours required to be considered eligible for employer discretionary contribution | hour	501
Percent rate for non-elective safe harbor contribution as component of profit sharing plan	3.00%
Cost of plan	$ 15,406,000	$ 10,100,000	$ 9,041,000
Age of Employee | year	50
Percentage of amount out of first specific percent of employee's contribution matched under plan	50.00%
Percentage of employee's contribution required to determine the matched amount under the plan	6.00%
Company's contribution to the plan	$ 4,037,000	3,224,000	2,946,000
401(k) and Profit Sharing Plan | Age Under 50
401(k) and Profit Sharing Plans
Maximum percentage of annual compensation allowable for contribution by eligible employees	60.00%
401(k) and Profit Sharing Plan | Age 50 and Over
401(k) and Profit Sharing Plans
Maximum percentage of annual compensation allowable for contribution by eligible employees	100.00%
Deferred Compensation Plan
401(k) and Profit Sharing Plans
Cost of plan	$ 502,000	481,000	431,000
Percentage of salary for deferral of cash payments	50.00%
Percentage of bonuses and directors fees for deferral of cash payments	100.00%
Total amount deferred	$ 803,000	739,000	967,000
Credit earning rate as a percentage of return on equity	50.00%
Deferred Compensation Plan Acquired
401(k) and Profit Sharing Plans
Cost of plan	$ 801,000	588,000	632,000
Liability related to obligations of deferred compensation plans	13,651,000	11,275,000
Supplemental Employee Retirement Plan
401(k) and Profit Sharing Plans
Cost of plan	122,000	105,000	85,000
Company's contribution to the plan	$ 423,000	$ 287,000	$ 299,000
Credit earning rate as a percentage of return on equity	50.00%