Summary of Significant Accounting Policies (Narrative) (Detail) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016
Cumulative Effect on Retained Earnings, Tax		$ 7.7
Excess Tax Benefit from Share-based Compensation, Operating Activities	$ 0.2

Amount of cash outflow for realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 20
-Section 55
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=65896087&loc=d3e11374-113907

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration