Common Dividends Declared Per Share (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Common stock	$ 0.75	$ 0.46	$ 0.30
Common OP units	$ 0.766	$ 0.470	$ 0.306

Cash dividends declared or paid to each outstanding limited partnership unit during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 4

-Section F

Name:	us-gaap_DistributionsPerLimitedPartnershipUnitOutstanding
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration