Commitments and Contingencies (Detail Textuals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure
Total rental expense, including short-term rentals	$ 17,112,000	$ 15,723,000	$ 20,658,000