Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Cost basis	$ 83,377
Unrealized gains
Unrealized losses	(80)
Recorded basis	83,297
Cash and cash equivalents	43,994	27,687	23,286	52,203
Short-term investments	39,303	36,605
Cash
Schedule of Available-for-sale Securities [Line Items]
Cost basis	28,674
Unrealized gains
Recorded basis	28,674
Cash and cash equivalents	28,674
Money Market Funds
Schedule of Available-for-sale Securities [Line Items]
Cost basis	15,320
Unrealized gains
Recorded basis	15,320
Cash and cash equivalents	15,320
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Cost basis	14,599
Unrealized gains
Unrealized losses	(1)
Recorded basis	14,598
Short-term investments	14,598
Corporate Bonds and Notes
Schedule of Available-for-sale Securities [Line Items]
Cost basis	24,784
Unrealized gains
Unrealized losses	(79)
Recorded basis	24,705
Short-term investments	$ 24,705