Fair Value Measurements (Details) (Fair value measured on a recurring basis [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value	$ 20,734	$ 28,604
Municipal Bonds [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value	18,278	23,697
Certificates of Deposit [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value	2,456	4,907
Level 1 [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value	20,734	28,604
Level 1 [Member] | Municipal Bonds [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value	18,278	23,697
Level 1 [Member] | Certificates of Deposit [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value	2,456	4,907
Level 2 [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value
Level 2 [Member] | Municipal Bonds [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value
Level 2 [Member] | Certificates of Deposit [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value
Level 3 [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value
Level 3 [Member] | Municipal Bonds [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value
Level 3 [Member] | Certificates of Deposit [Member]
Assets and liabilities measured at fair value on a recurring basis, by input level
Total assets at fair value