Equity and Noncontrolling Interests - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014 At-The-Market Common Equity Sales Program [Member]	Sep. 30, 2013 At-The-Market Common Equity Sales Program [Member]	Sep. 30, 2014 At-The-Market Common Equity Sales Program [Member]	Sep. 30, 2013 At-The-Market Common Equity Sales Program [Member]	May 31, 2012 At-The-Market Common Equity Sales Program [Member]
Equity And Noncontrolling Interests [Line Items]
Common stock, shares authorized	100,000,000	100,000,000	100,000,000						4,000,000
Sale of common stock, shares					0	0	0	0
Stock repurchase program, authorized amount				$ 200,000
Repurchased shares of common stock, shares	0	0	550,000
Repurchased shares of common stock, aggregate cost			24,800
Repurchased shares of common stock, average gross price			$ 45.08
Redeemable common units	6,190	6,190	6,121
Noncontrolling interests in the Operating Partnership, net book value	$ 2,760	$ 2,760	$ 2,792