Equity (Details) (USD $)	0 Months Ended			12 Months Ended							3 Months Ended	9 Months Ended		12 Months Ended		0 Months Ended			1 Months Ended		0 Months Ended		0 Months Ended			3 Months Ended								12 Months Ended		3 Months Ended								12 Months Ended		3 Months Ended								12 Months Ended					12 Months Ended
	Oct. 08, 2013	Aug. 28, 2012	May 10, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 19, 2013	Jun. 27, 2012	Jun. 27, 2012 Common Class A [Member]	Jun. 27, 2012 Common Class B [Member]	Sep. 30, 2013 Common Stock [Member]	Sep. 30, 2013 Common Stock [Member]	Oct. 09, 2012 Common Stock [Member]	Dec. 31, 2013 OP Units [Member]	Dec. 31, 2012 OP Units [Member]	Oct. 03, 2011 First Exchange Offer [Member] OP Units [Member]	Sep. 02, 2011 First Exchange Offer [Member] OP Units [Member]	Dec. 09, 2011 Second Exchange Offer [Member] Common Stock [Member]	Jan. 11, 2012 Second Exchange Offer [Member] OP Units [Member]	Dec. 09, 2011 Second Exchange Offer [Member] OP Units [Member]	Jun. 08, 2012 Third Exchange Offer [Member] Common Class A [Member]	May 10, 2012 Third Exchange Offer [Member] Common Class A [Member]	Jun. 08, 2012 Third Exchange Offer [Member] OP Units [Member]	Oct. 09, 2012 Third Exchange Offer [Member] OP Units [Member]	May 10, 2012 Third Exchange Offer [Member] OP Units [Member]	Dec. 31, 2013 Cash Distribution [Member]	Sep. 30, 2013 Cash Distribution [Member]	Jun. 30, 2013 Cash Distribution [Member]	Mar. 31, 2013 Cash Distribution [Member]	Dec. 31, 2012 Cash Distribution [Member]	Sep. 30, 2012 Cash Distribution [Member]	Jun. 30, 2012 Cash Distribution [Member]	Mar. 31, 2012 Cash Distribution [Member]	Dec. 31, 2013 Cash Distribution [Member]	Dec. 31, 2012 Cash Distribution [Member]	Dec. 31, 2013 Cash Distribution [Member] Common Stock [Member]	Sep. 30, 2013 Cash Distribution [Member] Common Stock [Member]	Jun. 30, 2013 Cash Distribution [Member] Common Stock [Member]	Mar. 31, 2013 Cash Distribution [Member] Common Stock [Member]	Dec. 31, 2012 Cash Distribution [Member] Common Stock [Member]	Sep. 30, 2012 Cash Distribution [Member] Common Stock [Member]	Jun. 30, 2012 Cash Distribution [Member] Common Stock [Member]	Mar. 31, 2012 Cash Distribution [Member] Common Stock [Member]	Dec. 31, 2013 Cash Distribution [Member] Common Stock [Member]	Dec. 31, 2012 Cash Distribution [Member] Common Stock [Member]	Dec. 31, 2013 Cash Distribution [Member] OP Units [Member]	Sep. 30, 2013 Cash Distribution [Member] OP Units [Member]	Jun. 30, 2013 Cash Distribution [Member] OP Units [Member]	Mar. 31, 2013 Cash Distribution [Member] OP Units [Member]	Dec. 31, 2012 Cash Distribution [Member] OP Units [Member]	Sep. 30, 2012 Cash Distribution [Member] OP Units [Member]	Jun. 30, 2012 Cash Distribution [Member] OP Units [Member]	Mar. 31, 2012 Cash Distribution [Member] OP Units [Member]	Dec. 31, 2013 Cash Distribution [Member] OP Units [Member]	Dec. 31, 2012 Cash Distribution [Member] OP Units [Member]	Oct. 08, 2013 Portion Attributable to Over-Allotment Option [Member]	Aug. 28, 2012 Portion Attributable to Over-Allotment Option [Member]	May 10, 2011 Portion Attributable to Over-Allotment Option [Member]	Dec. 31, 2013 ATM Program [Member] Common Stock [Member]
Class of Stock [Line Items]
Common shares, authorized (in shares)				400,000,000	400,000,000																			786,191
Common shares, par value per share (in dollars per share)	$ 0.001	$ 0.001		$ 0.001	$ 0.001				$ 0.001	$ 0.001			$ 0.001
Preferred shares, shares authorized (in shares)				50,000,000	50,000,000
Preferred shares, par value per share (in dollars per share)				$ 0.001	$ 0.001
Conversion ratio for class A common stock to class B common stock (in shares)								1
Common shares, issued (in shares)	4,000,000	4,830,000	5,310,000	21,943,700	16,943,098																																																			600,000	630,000	310,000
Share price of equity offering (in dollars per share)	$ 13.54	$ 12.8	$ 12
Proceeds from issuance of common shares, net of offering costs	$ 59,700,000	$ 58,700,000	$ 59,700,000	$ 63,887,000	$ 58,679,000	$ 59,683,000
Offering costs					3,100,000	4,000,000
OP units outstanding (in shares)														22,384,970	17,507,771		453,642			453,642		867,789			453,642
Conversion of stock, shares converted (in shares)														123,394	100,705	453,642			453,580		426,986		121,156
Common stock exchange offer, conversion basis for one share or unit (in shares)																		1
Ownership interest in operating partnership				97.50%
Conversion ratio for class A common stock to OP unit (in shares)				1
OP units owned (in shares)														21,822,878	16,822,285
Weighted-average share ownership in operating partnership				96.80%	94.10%	84.20%
Cash distribution paid (in dollars per share)																																				$ 0.285	$ 0.285	$ 0.2850	$ 0.2850	$ 0.2850	$ 0.2850	$ 0.2850	$ 0.2850	$ 1.14	$ 1.14	$ 0.2850	$ 0.2850	$ 0.2850	$ 0.2850	$ 0.2850	$ 0.2850	$ 0.2850	$ 0.2850	$ 1.14	$ 1.14
Cash distribution paid																										5,953,000	5,030,000	5,001,000	5,001,000	5,002,000	4,083,000	3,620,000	3,623,000	20,985,000	16,328,000	5,790,000	4,865,000	4,832,000	4,807,000	4,781,000	3,859,000	3,362,000	3,322,000	20,294,000	15,324,000	163,000	165,000	169,000	194,000	221,000	224,000	258,000	301,000	691,000	1,004,000
Equity Distribution Agreements, Authorized Amount							50,000,000
Stock Issued During Period, Shares, Issued for Cash												282,239
Proceeds from Issuance or Sale of Equity											4,200,000
Payments of Stock Issuance Costs				$ 40,000	$ 479,000	$ 0																																																					$ 200,000