Earnings per Common Share - Additional Information (Detail) - shares	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Dilutive shares related to convertible preferred stock	2,426,565	2,922,609	2,455,008	3,024,712

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible preferred stock using the if-converted method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 40
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e1930-109256

Name:	us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration