Fair Value - Presentation of Carrying Values and Fair Values of Certain of Company's Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets:
Investments, available-for-sale	$ 129,234	$ 125,085
Other investments	10,696	10,530
Liabilities:
Debentures payable	40,222	40,211
Carrying Value
Assets:
Investments, available-for-sale	129,234	125,085
Other investments	10,696	10,530
Liabilities:
Debentures payable	40,222	40,211
Fair Value
Assets:
Investments, available-for-sale	129,234	125,085
Other investments	10,696	10,530
Liabilities:
Debentures payable	$ 20,814	$ 19,606