Intangible Assets, net - Amortization Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amortization of Deferred Charges [Abstract]
Total amortization expenses	$ 2,777	$ 2,654	$ 2,367
Tradenames [Member]
Amortization of Deferred Charges [Abstract]
Total amortization expenses	0	0	330
Referral Relationships [Member]
Amortization of Deferred Charges [Abstract]
Total amortization expenses	2,161	1,934	1,512
Non-compete Agreements [Member]
Amortization of Deferred Charges [Abstract]
Total amortization expenses	$ 616	$ 720	$ 525