Financial Instruments - Additional Information (Detail) - USD ($)	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Expense related to increase in fair value of future expected contingent consideration	$ 0	$ (700,000)
Senior Notes \| 6.0% senior notes due 2022
Assets Sold under Agreements to Repurchase [Line Items]
Interest rate (as a percent)	6.00%

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant