Commitments and Contingencies - Maturities (Details) (USD $)	0 Months Ended	12 Months Ended
	Jan. 01, 2015 property item	Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012	Jan. 01, 2015
Leases with purchase options, annualized base rent receivables in next five years and thereafter
Leases with purchase option, annualized base rent receivables in 2015		$ 22,257,000
Leases with purchase option, annualized base rent receivables in 2016		33,188,000
Leases with purchase option, annualized base rent receivables in 2017		9,393,000
Leases with purchase option, annualized base rent receivables in 2018		18,697,000
Leases with purcase option, annualized base rent receivables in 2019		25,304,000
Leases with purchase option, annualized base rent receivables thereafter		64,918,000
Total leases with purchase option, annualized base rent receivables		173,757,000			5,000,000
Number of properties with purchase options, annualized base rent receivables
Number of properties with a purchase option, annualized base rent receivables in 2015		28
Number of properties with a purchase option, annualized base rent receivables in 2016		10
Number of properties with a purchase option, annualized base rent receivables in 2017		3
Number of properties with a purchase option, annualized base rent receivables in 2018		4
Number of properties with a purchase option, annualized base rent receivables in 2019		14
Number of properties with a purchase option, annualized base rent receivables thereafter		33
Total number of properties with a purchase option, annualized base rent receivables		92
Number of properties sold	8
Sale price of property	51,000,000
Rental Expense
Rental expense attributable to continuing operations		8,000,000	8,000,000	7,000,000
Maximum remaining term of ground leases excluding extension options		99 years
Future minimum lease obligations under non-cancelable ground and other operating leases
Future minimum lease obligations under non-cancelable ground and other operating leases, 2015		6,756,000
Future minimum lease obligations under non-cancelable ground and other operating leases, 2016		5,950,000
Future minimum lease obligations under non-cancelable ground and other operating leases, 2017		5,258,000
Future minimum lease obligations under non-cancelable ground and other operating leases, 2018		5,075,000
Future minimum lease obligations under non-cancelable ground and other operating leases, 2019		5,189,000
Future minimum lease obligations under non-cancelable ground and other operating leases, Thereafter		217,262,000
Future minimum lease obligations under non-cancelable ground and other operating leases, Total		$ 245,490,000