Employee Benefit Plans Employee Benefit Plans 12 (Details) - SERP - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance in Rabbi Trust
Balance in Rabbi Trust	$ 15,200
Fair value of assets held in Rabbi Trust	0	$ 0
Rabbi Trust | Level 1
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	15,227	11,996
Rabbi Trust | Level 2
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	0	0
Rabbi Trust | Level 3
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	0	0
Rabbi Trust | Cash equivalents | Level 1
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	45	46
Rabbi Trust | Cash equivalents | Level 2
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	0	0
Rabbi Trust | Cash equivalents | Level 3
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	0	0
Rabbi Trust | Fixed income fund | Level 1
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	6,072	4,801
Rabbi Trust | Fixed income fund | Level 2
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	0	0
Rabbi Trust | Fixed income fund | Level 3
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	0	0
Rabbi Trust | Equity securities | Level 1
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	9,110	7,149
Rabbi Trust | Equity securities | Level 2
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	0	0
Rabbi Trust | Equity securities | Level 3
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	0	0
Fair Value | Rabbi Trust
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	15,227	11,996
Fair Value | Rabbi Trust | Cash equivalents
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	45	46
Fair Value | Rabbi Trust | Fixed income fund
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	6,072	4,801
Fair Value | Rabbi Trust | Equity securities
Balance in Rabbi Trust
Fair value of assets held in Rabbi Trust	$ 9,110	$ 7,149