Fair Value, Balance Sheet Grouping (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Carrying Value [Member]
Assets [Abstract]
Limited partnerships	$ 62,668	$ 59,954
Liabilities [Abstract]
Short-term borrowings	10,000	10,000
Fair Value [Member]
Assets [Abstract]
Limited partnerships	62,668	59,954
Liabilities [Abstract]
Short-term borrowings	10,000	10,000
Fair Value [Member] | Level 1 [Member]
Assets [Abstract]
Limited partnerships	0	0
Liabilities [Abstract]
Short-term borrowings	0	0
Fair Value [Member] | Level 2 [Member]
Assets [Abstract]
Limited partnerships	0	0
Liabilities [Abstract]
Short-term borrowings	10,000	10,000
Fair Value [Member] | Level 3 [Member]
Assets [Abstract]
Limited partnerships	62,668	59,954
Liabilities [Abstract]
Short-term borrowings	$ 0	$ 0