Investments and Marketable Securities - Schedule of Realized Gains on Sales of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Available For Sale Securities [Abstract]
Proceeds	$ 336,741	$ 164,410	$ 303,801
Realized gains	727	423	388
Realized losses	(81)	(78)	(306)
Net realized gains included in other comprehensive income (loss) as of the end of the prior year	$ 603	$ 285	$ 159