Marketable Securities - Summary of Company Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 127,643	$ 133,724
Unrealized Gains	35	700
Unrealized Losses	(172)	(298)
Fair Value	127,506	134,126
Common Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		300
Unrealized Gains		618
Fair Value		918
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	127,643	133,424
Unrealized Gains	35	82
Unrealized Losses	(172)	(298)
Fair Value	$ 127,506	$ 133,208

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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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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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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-Publisher FASB
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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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