Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Common Stock Class A Non-voting
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01000
Common stock, shares authorized (shares)	100,000,000	100,000,000	100,000,000
Common stock, shares issued (shares)	51,494,246	51,427,832	51,306,608
Common stock, shares outstanding (shares)	51,494,246	51,427,832	51,306,608
Common Stock Class B Voting
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01000
Common stock, shares authorized (shares)	3,000,000	3,000,000	3,000,000
Common stock, shares issued (shares)	2,970,171	2,970,171	2,970,171.000
Common stock, shares outstanding (shares)	2,970,171	2,970,171	2,970,171