CONSOLIDATED STATEMENTS OF INCOME (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CONSOLIDATED STATEMENTS OF INCOME
Rental income from a lessee that qualifies as a related party	$ 4,370	$ 4,264	$ 4,160
Straight-line rental income from a lessee that qualifies as a related party	131	238	342
Interest income from an entity that qualifies as a related party	$ 235	$ 721	$ 720