Earnings Per Share and Dividends - Additional Information (Details) - USD ($)		3 Months Ended
	May 31, 2017	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Dividends Payable [Line Items]
Dividends declared and paid		$ 3,184,000
Common Class A
Dividends Payable [Line Items]
Common stock, shares outstanding		17,683,429		17,652,548
Cash dividends declared per share of Class A common stock		$ 0.18	$ 0.15
Common Class B
Dividends Payable [Line Items]
Common stock, shares outstanding		1		1
Quarterly dividend | Common Class A
Dividends Payable [Line Items]
Cash dividends declared per share of Class A common stock	$ 0.18	$ 0.18	$ 0.15
Dividends declared and paid		$ 3,184,000	$ 2,638,000
Non-controlling interest | Quarterly dividend | Common Class A
Dividends Payable [Line Items]
Distributions declared to non-controlling unitholders		$ 2,261,000	$ 1,884,000