Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss)
Balance	$ 9,645	$ 47,962	$ 33,487
Other comprehensive income (loss) before reclassification	7,366	(38,500)	14,475
Amounts reclassified from accumulated other comprehensive income	733	183	0
Net current period other comprehensive income (loss)	8,099	(38,317)	14,475
Balance	17,744	9,645	47,962
Available-For-Sale Securities
Accumulated Other Comprehensive Income (Loss)
Balance	8,485	58,245	38,928
Other comprehensive income (loss) before reclassification	19,335	(49,943)	19,317
Amounts reclassified from accumulated other comprehensive income	125	183	0
Net current period other comprehensive income (loss)	19,460	(49,760)	19,317
Balance	27,945	8,485	58,245
Derivatives Used for Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Balance	1,160	(10,283)	(5,441)
Other comprehensive income (loss) before reclassification	(11,969)	11,443	(4,842)
Amounts reclassified from accumulated other comprehensive income	608	0	0
Net current period other comprehensive income (loss)	(11,361)	11,443	(4,842)
Balance	$ (10,201)	$ 1,160	$ (10,283)