Summary of Significant Accounting Policies (Summary of Activity Recorded within the Allowance for Doubtful Accounts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning balance	$ 5,272	$ 4,868	$ 4,280
Bad debt expense	1,253	2,519	1,404
Accounts written off and other adjustments	(91)	(2,115)	(816)
Ending balance	$ 6,434	$ 5,272	$ 4,868