Fair Value Measurements - Additional Information (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Fair Value Measurement [Line Items]
Unrealized gains on the investments after-tax	$ 392,000	$ 275,000
Money Market Funds [Member]
Fair Value Measurement [Line Items]
Investments	16,700,000	10,200,000
Unrealized gains on the investments	0	0
Other Mutual Funds [Member]
Fair Value Measurement [Line Items]
Investments	1,300,000	1,200,000
Unrealized gains on the investments	641,000	450,000
Unrealized gains on the investments after-tax	$ 392,000	$ 275,000