Cash Equivalents and Investments (Summary of Cash and Available-For-Sale Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	$ 168,679	$ 227,902
Unrealized Gains	10	88
Unrealized Losses	0	(44)
Total, Fair Value	168,689	227,946
Cash and Cash Equivalents	131,212	168,544	211,574	303,227
Restricted Investment	20,000	0
Short-Term Marketable Securities	17,477	42,301
Long-Term Marketable Securities	0	17,101
Cash and Cash Equivalents [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	7,894	3,177
Unrealized Gains	0	0
Unrealized Losses	0	0
Total, Fair Value	7,894	3,177
Cash and Cash Equivalents	7,894	3,177
Restricted Investment	0	0
Short-Term Marketable Securities	0	0
Long-Term Marketable Securities	0	0
Money market funds [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	121,095	163,368
Unrealized Gains	0	0
Unrealized Losses	0	0
Total, Fair Value	121,095	163,368
Cash and Cash Equivalents	121,095	163,368
Restricted Investment	0	0
Short-Term Marketable Securities	0	0
Long-Term Marketable Securities	0	0
Certificates Of Deposit [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	26,128
Unrealized Gains	0
Unrealized Losses	0
Total, Fair Value	26,128
Cash and Cash Equivalents	2,223
Restricted Investment	20,000
Short-Term Marketable Securities	3,905
Long-Term Marketable Securities	0
Corporate debt securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	13,562	44,863
Unrealized Gains	10	57
Unrealized Losses	0	(43)
Total, Fair Value	13,572	44,877
Cash and Cash Equivalents	0	0
Restricted Investment	0	0
Short-Term Marketable Securities	13,572	27,776
Long-Term Marketable Securities	0	17,101
Commercial Paper [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost		8,997
Unrealized Gains		0
Unrealized Losses		(1)
Total, Fair Value		8,996
Cash and Cash Equivalents		1,999
Restricted Investment		0
Short-Term Marketable Securities		6,997
Long-Term Marketable Securities		0
US Government Agencies Debt Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	0	2,003
Unrealized Gains	0	12
Unrealized Losses	0	0
Total, Fair Value	0	2,015
Cash and Cash Equivalents	0	0
Restricted Investment	0	0
Short-Term Marketable Securities	0	2,015
Long-Term Marketable Securities	0	0
US Treasury Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	0	5,494
Unrealized Gains	0	19
Unrealized Losses	0	0
Total, Fair Value	0	5,513
Cash and Cash Equivalents	0	0
Restricted Investment	0	0
Short-Term Marketable Securities	0	5,513
Long-Term Marketable Securities	$ 0	$ 0