Investments - Summary of Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investments Schedule [Abstract]
Marketable securities	$ 40,136	$ 50,251
Equity method investments	9,194	7,209
Nonqualified retirement plan assets	4,970	5,063
Other investments	925	925
Total investments	$ 55,225	$ 63,448