Dividends (Details Textual) - USD ($) $ / shares in Units, $ in Thousands									1 Months Ended					3 Months Ended		9 Months Ended
	Sep. 13, 2017	Jun. 09, 2017	May 03, 2017	Apr. 14, 2017	Mar. 03, 2017	Jul. 08, 2016	Jun. 01, 2016	Mar. 02, 2016	Dec. 23, 2016	Nov. 21, 2016	Sep. 30, 2016	Aug. 30, 2016	Apr. 15, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Common Stock, Dividends, Per Share, Declared														$ 0.30	$ 0.30	$ 0.90	$ 0.80
Dividends Payable, Date to be Paid	Oct. 13, 2017
Dividends Payable, Date of Record														Sep. 25, 2017
Dividends				$ 1,800		$ 1,500			$ 2,900		$ 1,800		$ 1,500
Dividends Payable														$ 1,800		$ 1,800
Payments of Ordinary Dividends, Common Stock		$ 1,800														$ 3,541	$ 4,688
Dividends Payable, Date Declared	Sep. 13, 2017
Common Class A [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.30		$ 0.30		$ 0.30		$ 0.25	$ 0.25		$ 0.30		$ 0.30
Common Class B [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.30									$ 0.20