Investments - Components of Net Realized and Unrealized Gains (Losses) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Investments Debt And Equity Securities [Abstract]
Gross realized gains on available-for-sale securities	$ 26	$ 65
Gross realized losses on available-for-sale securities	(145)	(17)
Net realized gains on trading securities	5,917	6,009
Net unrealized gains on trading securities	11,778	5,132
Net realized and unrealized gains on other investments	16,997	18,931
Net realized and unrealized gains	34,573	30,120
Proceeds from sales and maturities of available-for-sale securities	$ 59,238	$ 59,631