Fair Value - Presentation of Carrying Values and Fair Values of Certain Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Investments, available-for-sale	$ 129,945	$ 117,212
Other investments	9,750	9,994
Carrying Value
Assets:
Investments, available-for-sale	129,945	117,212
Other investments	9,750	9,994
Liabilities:
Debentures payable	40,348	40,302
Term loan from principal stockholder	29,805	29,779
Fair Value
Assets:
Investments, available-for-sale	129,945	117,212
Other investments	9,750	9,994
Liabilities:
Debentures payable	21,248	11,488
Term loan from principal stockholder	$ 26,691	$ 15,000