Fair Value Measurements - Summary of Short-Term and Long-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	$ 353,109	$ 328,796
Gross Unrealized Gains	582	1,038
Gross Unrealized Losses	(723)	(499)
Estimated Fair Value	352,968	329,335
U.S. Government and Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	89,617	96,913
Gross Unrealized Gains	27	77
Gross Unrealized Losses	(18)	(3)
Estimated Fair Value	89,626	96,987
Obligations of Government-Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	33,506	4,830
Gross Unrealized Gains	5	10
Gross Unrealized Losses	(1)	0
Estimated Fair Value	33,510	4,840
State and Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	51,573	96,383
Gross Unrealized Gains	82	161
Gross Unrealized Losses	(28)	(28)
Estimated Fair Value	51,627	96,516
Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	166,642	130,634
Gross Unrealized Gains	453	790
Gross Unrealized Losses	(675)	(468)
Estimated Fair Value	166,420	130,956
Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	11,771	36
Gross Unrealized Gains	15	0
Gross Unrealized Losses	(1)	0
Estimated Fair Value	$ 11,785	$ 36