Investments Fair Value and Gross Unrealized Losses of Available for Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains	$ 8,065	$ 6,984	$ 628
Available-for-sale Securities, Gross Realized Losses	(4,300)	(4,376)	(346)
Available-for-sale Securities, Net Realized Gain (Loss)	3,765	2,608	282
Unrealized loss position, Less than 12 Months, fair value		26,086
Unrealized loss position, Less than 12 Month, Gross Unrealized Losses		(5,033)
Unrealized loss position, 12 Months or Greater, Fair Value		803
Unrealized loss position, 12 Month or Greater, Gross Unrealized Losses		(451)
Unrealized loss position, Total, Fair Value	58,272	26,889
Unrealized loss position, Total, Gross Unrealized Losses	(27,495)	(5,484)
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized loss position, Less than 12 Months, fair value		15,609
Unrealized loss position, Less than 12 Month, Gross Unrealized Losses		(4,757)
Unrealized loss position, 12 Months or Greater, Fair Value		803
Unrealized loss position, 12 Month or Greater, Gross Unrealized Losses		(451)
Unrealized loss position, Total, Fair Value	39,869	16,412
Unrealized loss position, Total, Gross Unrealized Losses	(23,732)	(5,208)
Corporate obligations
Schedule of Available-for-sale Securities [Line Items]
Unrealized loss position, Less than 12 Months, fair value		10,477
Unrealized loss position, Less than 12 Month, Gross Unrealized Losses		(276)
Unrealized loss position, 12 Months or Greater, Fair Value		0
Unrealized loss position, 12 Month or Greater, Gross Unrealized Losses		0
Unrealized loss position, Total, Fair Value	13,530	10,477
Unrealized loss position, Total, Gross Unrealized Losses	(3,441)	(276)
Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Unrealized loss position, Total, Fair Value	4,873
Unrealized loss position, Total, Gross Unrealized Losses	$ (322)	$ 0

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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