Schedule of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 79,543	$ 45,341
Unrealized Gains	117	131
Unrealized Losses	(42)	(12)
Fair Value	79,618	45,460
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	47,325	30,488
Unrealized Gains	60	48
Unrealized Losses	(28)	(10)
Fair Value	47,357	30,526
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29,776	14,853
Unrealized Gains	56	83
Unrealized Losses	(9)	(2)
Fair Value	29,823	14,934
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,442
Unrealized Gains	1
Unrealized Losses	(5)
Fair Value	$ 2,438