Investments - Summary of Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Investments Schedule [Abstract]
Marketable securities	$ 79,505	$ 41,496
Equity method investments	10,145	9,007
Nonqualified retirement plan assets	5,319	5,310
Other investments	925	925
Total investments	$ 95,894	$ 56,738