Schedule of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 70,008	$ 45,341
Unrealized Gains	76	131
Unrealized Losses	(118)	(12)
Fair Value	69,966	45,460
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	38,222	30,488
Unrealized Gains	34	48
Unrealized Losses	(43)	(10)
Fair Value	38,213	30,526
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,282	14,853
Unrealized Gains	42	83
Unrealized Losses	(71)	(2)
Fair Value	30,253	14,934
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,504
Unrealized Losses	(4)
Fair Value	$ 1,500