Cash Equivalents and Investments (Summary of Cash and Available-For-Sale Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	$ 278,849		$ 168,679
Unrealized Gains	1		10
Unrealized Losses	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	278,850		168,689
Cash and Cash Equivalents	251,473	[1]	131,212	[2]	184,506	168,544
Restricted Investment	20,000		20,000
Short-Term Marketable Securities	7,377	[1]	17,477	[2]
Cash [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	11,217		7,894
Unrealized Gains	0		0
Unrealized Losses	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	11,217		7,894
Cash and Cash Equivalents	11,217		7,894
Restricted Investment	0		0
Short-Term Marketable Securities	0		0
Money Market Funds [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	240,256		121,095
Unrealized Gains	0		0
Unrealized Losses	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	240,256		121,095
Cash and Cash Equivalents	240,256		121,095
Restricted Investment	0		0
Short-Term Marketable Securities	0		0
Certificate of Deposit [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	26,375		26,128
Unrealized Gains	0		0
Unrealized Losses	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	26,375		26,128
Cash and Cash Equivalents	0		2,223
Restricted Investment	20,000		20,000
Short-Term Marketable Securities	6,375		3,905
Corporate Debt Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	1,001		13,562
Unrealized Gains	1		10
Unrealized Losses	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	1,002		13,572
Cash and Cash Equivalents	0		0
Restricted Investment	0		0
Short-Term Marketable Securities	$ 1,002		$ 13,572

[1] unaudited

[2] Note 1