Accounting Policies - Principles of Consolidation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013 subsidiary	Dec. 31, 2012
Schedule of Summary of Significant Accounting Policies [Line Items]
Number of Subsidiaries										3
Guarantee and commitment fees	$ 6,094	$ 6,172	$ 6,403	$ 6,518	$ 6,768	$ 6,819	$ 6,759	$ 6,612	$ 25,187	$ 26,958	$ 24,963
Guarantor Subsidiaries [Member]
Schedule of Summary of Significant Accounting Policies [Line Items]
Guarantee and commitment fees									$ 10,100	$ 10,900	$ 10,300