Marketable Investments - Summary of Company's Marketable Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 80,988	$ 145,512
Gross Unrealized Gains	117	407
Gross Unrealized Losses	(92)	(2,073)
Total	81,013	143,846
State and Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,809	18,859
Gross Unrealized Gains	5	27
Gross Unrealized Losses		(14)
Total	6,814	18,872
Federal Agency and Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	74,179	115,653
Gross Unrealized Gains	112	380
Gross Unrealized Losses	(92)	(29)
Total	74,199	116,004
Total Short-Term Available-for-Sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		134,512
Gross Unrealized Gains		407
Gross Unrealized Losses		(43)
Total		134,876
ARS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,000	11,000
Gross Unrealized Gains
Gross Unrealized Losses		(2,030)
Total		$ 8,970