Fair Value - Presentation of Carrying Values and Fair Values of Certain Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets:
Investments, available-for-sale	$ 133,448	$ 117,212
Other investments	10,486	9,994
Carrying Value
Assets:
Investments, available-for-sale	133,448	117,212
Other investments	10,486	9,994
Liabilities:
Debentures payable	40,336	40,302
Term loan from principal stockholder	29,799	29,779
Fair Value
Assets:
Investments, available-for-sale	133,448	117,212
Other investments	10,486	9,994
Liabilities:
Debentures payable	17,375	11,488
Term loan from principal stockholder	$ 22,114	$ 15,000