Investments - Fair value and gross unrealized losses of the available for sale securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Gross realized gains	$ 3,196	$ 2,607	$ 6,396	$ 3,865
Gross realized losses	(1,120)	(3,852)	(1,329)	(3,894)
Realized gains (losses), net	2,076	(1,245)	5,067	(29)
Unrealized loss position less than 12 months, fair value	25,263		25,263		26,086
Unrealized loss position, less than 12 month, gross unrealized losses			(3,500)		(5,033)
Unrealized loss position, 12 months or greater, fair value	199		199		803
Unrealized loss position, 12 month or greater, gross unrealized losses			(233)		(451)
Unrealized loss position, total, fair value	25,462		25,462		26,889
Unrealized loss position, total, gross unrealized losses			(3,733)		(5,484)
Corporate securities
Unrealized loss position less than 12 months, fair value	19,244		19,244		15,609
Unrealized loss position, less than 12 month, gross unrealized losses			(3,481)		(4,757)
Unrealized loss position, 12 months or greater, fair value	199		199		803
Unrealized loss position, 12 month or greater, gross unrealized losses			(233)		(451)
Unrealized loss position, total, fair value	19,443		19,443		16,412
Unrealized loss position, total, gross unrealized losses			(3,714)		(5,208)
Corporate obligations
Unrealized loss position less than 12 months, fair value	6,019		6,019		10,477
Unrealized loss position, less than 12 month, gross unrealized losses			(19)		(276)
Unrealized loss position, 12 months or greater, fair value	0		0		0
Unrealized loss position, 12 month or greater, gross unrealized losses			0		0
Unrealized loss position, total, fair value	6,019		6,019		10,477
Unrealized loss position, total, gross unrealized losses			$ (19)		$ (276)