Related Party and Affiliated Real Estate Joint Venture Transactions - Summarized Information of Management Fee Revenues for Related Party and Affiliated Joint Ventures (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Related Party Transaction [Line Items]
Management fee revenues	$ 28,215	$ 26,614	$ 25,706
ESW [Member]
Related Party Transaction [Line Items]
Management fee revenues	480	450	430
ESW II [Member]
Related Party Transaction [Line Items]
Management fee revenues	410	382	354
ESNPS [Member]
Related Party Transaction [Line Items]
Management fee revenues	550	528	498
ESSM [Member]
Related Party Transaction [Line Items]
Management fee revenues	132	117	107
HSRE-ESP IA, LLC (HSRE) [Member]
Related Party Transaction [Line Items]
Management fee revenues	1,201	1,146	1,094
PRISA [Member]
Related Party Transaction [Line Items]
Management fee revenues	5,466	5,215	5,174
PRISA II [Member]
Related Party Transaction [Line Items]
Management fee revenues	4,635	4,397	4,138
VRS [Member]
Related Party Transaction [Line Items]
Management fee revenues	1,326	1,286	1,207
WCOT [Member]
Related Party Transaction [Line Items]
Management fee revenues	1,680	1,601	1,520
SPI [Member]
Related Party Transaction [Line Items]
Management fee revenues	1,999	1,953	1,885
Other [Member]
Related Party Transaction [Line Items]
Management fee revenues	$ 10,336	$ 9,539	$ 9,299