Common Stock and Class B Common Stock (Detail) - USD ($) $ in Thousands			1 Months Ended	12 Months Ended
	Apr. 27, 2016	Jan. 26, 2016	Apr. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Conversion of Stock [Line Items]
Additional cash issued to class B common stock holders				$ 12,000	$ 0	$ 0
Number of treasury shares held (shares)				352,161	352,161
Subsidiaries
Conversion of Stock [Line Items]
Number of treasury shares held (shares)				145,820	145,820
Conversion, Class B Common Stock To Common Stock
Conversion of Stock [Line Items]
Additional cash issued to class B common stock holders	$ 12,000	$ 12,000	$ 12,000	$ 12,000
Conversion, Class B Common Stock To Common Stock | Class B Common Stock
Conversion of Stock [Line Items]
Number of shares converted (shares)	1,050,012	1,050,012
Conversion, Class B Common Stock To Common Stock | Common Stock
Conversion of Stock [Line Items]
Number of shares issued (shares)	1,050,012	1,050,012