Summary of Proceeds and Realized Gains/(Losses) on Equity Securities and Certificates of Deposit (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Duration Of Unrealized Losses On Equity Securities [Line Items]
Proceeds	$ 10,654	$ 12,950	$ 9,327
Gross Realized Gains	13	124	6
Gross Realized Losses