Deferred costs and other intangibles - Amortization Expense Related to Deferred Costs and Other Intangibles (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Finite-Lived Intangible Assets [Line Items]
Total	$ 24,518
Value of In-place Leases [Member]
Finite-Lived Intangible Assets [Line Items]
Remaining 2013	1,521
2014	2,835
Total	4,356
Trademark [Member]
Finite-Lived Intangible Assets [Line Items]
Remaining 2013	165
2014	659
2015	660
2016	659
2017	659
Thereafter	93
Total	2,895
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Remaining 2013	75
2014	300
2015	300
2016	300
2017	300
Thereafter	732
Total	2,007
Deferred Leasing Costs [Member]
Finite-Lived Intangible Assets [Line Items]
Remaining 2013	2,291
2014	3,931
Total	6,222
Deferred Financing Costs [Member]
Finite-Lived Intangible Assets [Line Items]
Remaining 2013	584
2014	2,316
2015	2,316
2016	2,322
2017	984
Thereafter	516
Total	$ 9,038