Common Stock and Treasury Stock (Details Textual)	3 Months Ended
	Mar. 31, 2018 USD ($) shares
Common Stock [Line Items]
Share repurchase program, authorized amount	$ 75,800,000
Stock repurchase program, remaining authorization amount	$ 22,300,000
Stock Buy-Back Program [Member]
Common Stock [Line Items]
Stock Repurchased During Period, Shares | shares	2,500
Stock Repurchased During Period, Value	$ 93,000