Schedule of Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 106,144	$ 96,735
Unrealized Gains	40	59
Unrealized Losses	(116)	(163)
Fair Value	106,068	96,631
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	35,493	27,820
Unrealized Gains	20	52
Unrealized Losses	(43)	(17)
Fair Value	35,470	27,855
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	66,520	65,487
Unrealized Gains	14	5
Unrealized Losses	(72)	(144)
Fair Value	66,462	65,348
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,131	3,428
Unrealized Gains	6	2
Unrealized Losses	(1)	(2)
Fair Value	$ 4,136	$ 3,428