Marketable Securities - Summary of Company Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 133,724	$ 162,970
Unrealized Gains	700	40
Unrealized Losses	(298)	(759)
Fair Value	134,126	162,251
Common Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	300	3
Unrealized Gains	618	36
Fair Value	918	39
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	133,424	157,977
Unrealized Gains	82	4
Unrealized Losses	(298)	(759)
Fair Value	$ 133,208	157,222
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		4,990
Fair Value		$ 4,990

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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-Publisher FASB
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