Investments - Investments in Continuous Unrealized Loss Position for Less Than Twelve Months (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 132,230	$ 30,332
Unrealized Losses	(137)	(30)
US Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,999
Unrealized Losses	(1)
Corporate bonds and notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	130,231	30,332
Unrealized Losses	$ (136)	$ (30)