Employee Benefit Plans (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) executive	Dec. 31, 2016 USD ($) executive	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [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 vesting rate (as a percent)	20.00%
Matching contribution, vesting period	5 years
Employer's contribution	$ 8,900	$ 8,400	$ 7,500
Supplemental Executive Retirement Plan (SERP)
Defined Benefit Plan Disclosure [Line Items]
Number of executives remaining under the SERP | executive	1	1
Accrued benefit expense	$ 331	$ 624	$ 619
Benefit obligation	$ 4,200	$ 4,100