Fair Value Measurements - Additional Information (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Fair Value Measurement [Line Items]
Unrealized gains on the investments after-tax	$ 330,000	$ 275,000
Money Market Funds [Member]
Fair Value Measurement [Line Items]
Investments	7,200,000	10,200,000
Unrealized gains on the investments	0	0
Other Mutual Funds [Member]
Fair Value Measurement [Line Items]
Investments	1,200,000	1,200,000
Unrealized gains on the investments	540,000	450,000
Unrealized gains on the investments after-tax	$ 330,000	$ 275,000