Employee Benefit Plans (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) executive	Dec. 31, 2017 USD ($) executive	Dec. 31, 2016 USD ($)
Employee Benefit Plan [Line Items]
Maximum employee contribution (as a percent)	80.00%
Company match percentage (as a percent)	75.00%
Percentage of employee pay that Company matches (as a percent)	6.00%
Matching contribution annual vesting rate (as a percent)	20.00%
Matching contribution, vesting period	5 years
Employer's contribution	$ 9,900,000	$ 8,900,000	$ 8,400,000
Supplemental Executive Retirement Plan (SERP)
Employee Benefit Plan [Line Items]
Additional benefits to be accrued for	$ 0
Number of executives remaining under the SERP | executive	1	1
Accrued benefit expense	$ 332,000	$ 331,000	$ 624,000
Benefit obligation	$ 4,200,000	$ 4,200,000