Schedule of Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 101,570	$ 126,257
Unrealized Gains	188	9
Unrealized Losses	(25)	(214)
Fair Value	101,733	126,052
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	50,156	57,394
Unrealized Gains	103	7
Unrealized Losses	(10)	(66)
Fair Value	50,249	57,335
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	49,513	66,960
Unrealized Gains	84	2
Unrealized Losses	(15)	(147)
Fair Value	49,582	66,815
Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,901	1,903
Unrealized Gains	1
Unrealized Losses		(1)
Fair Value	$ 1,902	$ 1,902