Fair Value of Financial Assets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	$ 48,367	$ 64,312
Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	4,869	7,270
Corporate Bond Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	27,454	23,193
U.S. Federal Agencies
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	14,143	27,251
Foreign Bonds and Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value		4,696
Municipal Obligations
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	1,901	1,902
Fair Value, Inputs, Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	4,869	7,270
Fair Value, Inputs, Level 1 | Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	4,869	7,270
Fair Value, Inputs, Level 1 | Corporate Bond Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 1 | U.S. Federal Agencies
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 1 | Foreign Bonds and Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 1 | Municipal Obligations
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	43,498	57,042
Fair Value, Inputs, Level 2 | Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 2 | Corporate Bond Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	27,454	23,193
Fair Value, Inputs, Level 2 | U.S. Federal Agencies
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	14,143	27,251
Fair Value, Inputs, Level 2 | Foreign Bonds and Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value		4,696
Fair Value, Inputs, Level 2 | Municipal Obligations
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	1,901	1,902
Fair Value, Inputs, Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 3 | Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 3 | Corporate Bond Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 3 | U.S. Federal Agencies
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 3 | Foreign Bonds and Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value
Fair Value, Inputs, Level 3 | Municipal Obligations
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value