Cash Equivalents and Investments (Summary of Cash and Available-For-Sale Securities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2015		Dec. 31, 2014		Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	$ 229,061		$ 293,127
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	621		560
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	229,682		293,687
Cash and Cash Equivalents	227,855	[1],[2]	291,377	[3]	$ 281,607	$ 94,302
Short-Term Marketable Securities	1,827	[1]	2,310	[3]
Cash [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	88,005		69,585
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	0		0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	88,005		69,585
Cash and Cash Equivalents	88,005		69,585
Short-Term Marketable Securities	0		0
Money Market Funds [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	139,850		221,792
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	0		0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	139,850		221,792
Cash and Cash Equivalents	139,850		221,792
Short-Term Marketable Securities	0		0
Equity Securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Adjusted Cost	1,206		1,750
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	621		560
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0		0
Cash, Cash Equivalents and Available-for-Sale Securities, Fair Value	1,827		2,310
Cash and Cash Equivalents	0		0
Short-Term Marketable Securities	$ 1,827		$ 2,310

[1] unaudited

[2] unaudited

[3] Note 1