Borrowings Under Line of Credit Arrangement and Related Items (Tables)

12 Months Ended

Dec. 31, 2010

Borrowings Under Line of Credit Arrangement and Related Items (Tables) [Abstract]

Aggregate borrowings under the unsecured line of credit arrangement

	Year Ended December 31,
	2010			2009			2008
Balance outstanding at quarter end	$	300,000		$	140,000		$	570,000
Maximum amount outstanding at any month end	$	560,000		$	559,000		$	744,000
Average amount outstanding (total of daily principal balances divided by days in period)	$	268,762		$	241,463		$	500,561
Weighted average interest rate (actual interest expense divided by average borrowings outstanding)		1.48	%		1.92	%		3.77	%