Goodwill and Intangible Assets (Details Textuals)	3 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) acquisition	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Goodwill, Impairment Loss			$ 0	$ 0	$ 0
Goodwill acquired during period	$ 4,000,000	$ 55,000
Goodwill	976,239,000		$ 976,239,000	$ 971,951,000
Additions to finite-lived intangible assets	$ 2,000,000	162,000
Number of Acquisitions | acquisition			2
Customer Relationships [Member]
Business Acquisition [Line Items]
Additions to finite-lived intangible assets		$ 162,000