Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of assets and liabilities measured at fair value on recurring basis
Interest rate swaps	$ 568	$ 510
Level 1 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Interest rate swaps	0	0
Level 2 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Interest rate swaps	568	510
Level 3 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Interest rate swaps	0	0
Money market mutual funds [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	11,027	8,818
Money market mutual funds [Member] | Level 1 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	11,027	8,818
Money market mutual funds [Member] | Level 2 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	0	0
Money market mutual funds [Member] | Level 3 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	0	0
Government agency bonds [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	4,077	9,015
Government agency bonds [Member] | Level 1 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	4,077	9,015
Government agency bonds [Member] | Level 2 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	0	0
Government agency bonds [Member] | Level 3 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	0	0
Corporate notes [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	4,004	3,019
Corporate notes [Member] | Level 1 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	4,004	3,019
Corporate notes [Member] | Level 2 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	0	0
Corporate notes [Member] | Level 3 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	0	0
United States treasuries [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	3,687
United States treasuries [Member] | Level 1 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	3,687
United States treasuries [Member] | Level 2 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	0
United States treasuries [Member] | Level 3 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	0
Certificates of deposit [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	1,501	2,701
Certificates of deposit [Member] | Level 1 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	1,501	2,701
Certificates of deposit [Member] | Level 2 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	0	0
Certificates of deposit [Member] | Level 3 [Member]
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	$ 0	$ 0