Fair Value - Presentation of Carrying Values and Fair Values of Certain of Company's Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets:
Investments, available-for-sale	$ 125,085	$ 130,248
Other investments	10,530	7,513
Liabilities:
Debentures payable	40,341	40,301
Carrying Value [Member]
Assets:
Investments, available-for-sale	125,085	130,248
Other investments	10,530	7,513
Liabilities:
Debentures payable	40,341	40,301
Fair Value [Member]
Assets:
Investments, available-for-sale	125,085	130,248
Other investments	10,530	7,513
Liabilities:
Debentures payable	$ 19,606	$ 15,006