Schedule of Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 126,631	$ 96,735
Unrealized Gains	138	59
Unrealized Losses	(31)	(163)
Fair Value	126,738	96,631
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	52,207	27,820
Unrealized Gains	110	52
Unrealized Losses		(17)
Fair Value	52,317	27,855
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	71,530	65,487
Unrealized Gains	25	5
Unrealized Losses	(31)	(144)
Fair Value	71,524	65,348
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,894	3,428
Unrealized Gains	3	2
Unrealized Losses		(2)
Fair Value	$ 2,897	$ 3,428