Debt and Financing Arrangements - Summary of Unsecured Credit Facility (Detail)	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Weighted average rates	2.43%	2.02%
Minimum [Member]
Debt Instrument [Line Items]
Range of effective rates	1.82%	1.65%
Maximum [Member]
Debt Instrument [Line Items]
Range of effective rates	3.75%	3.50%

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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