Cash Equivalents and Investments (Summary of Cash and Available-For-Sale Securities) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016		Dec. 31, 2015		Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	$ 221,792		$ 219,682
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	0		670
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	221,792		220,352
Cash and cash equivalents	115,854	[1],[2]	218,883	[3]	$ 292,065	$ 291,377
Available-for-sale Securities, Restricted			0
Restricted Cash and Investments, Current	105,938
Short-Term Marketable Securities	0	[1]	1,469	[3]
Cash [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	162,162		124,082
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	162,162		124,082
Cash and cash equivalents	56,224		124,082
Available-for-sale Securities, Restricted	105,938		0
Short-Term Marketable Securities	0		0
Money Market Funds [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	59,630		94,801
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	59,630		94,801
Cash and cash equivalents	59,630		94,801
Available-for-sale Securities, Restricted	0		0
Short-Term Marketable Securities	$ 0		0
Equity Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost			799
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax			670
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value			1,469
Cash and cash equivalents			0
Short-Term Marketable Securities			$ 1,469

[1] unaudited

[2] unaudited

[3] Note 1