Employee Benefit Plans Employee Benefit Plans 17 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Employer's contribution	$ 2,300	$ 2,200	$ 2,100
Employer discretionary contribution amount	$ 1,100	$ 951	$ 755