Accumulated Other Comprehensive Income (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reclassifications out of accumulated other comprehensive income, net of tax
Interest expense	$ (4,029)	$ (2,625)	$ (8,643)	$ (8,743)
Provision for income taxes	(6,804)	(4,938)	(18,151)	(12,576)
Net income available to common shareholders	11,512	9,063	34,693	24,121
Total reclassifications for the period			(142)
Gains and losses on cash flow hedges
Reclassifications out of accumulated other comprehensive income, net of tax
Total reclassifications for the period			(142)
Gains and losses on cash flow hedges | Interest rate contracts
Reclassifications out of accumulated other comprehensive income, net of tax
Total reclassifications for the period			142
Gains and losses on cash flow hedges | Amount Reclassified from Accumulated Other Comprehensive Income | Interest rate contracts
Reclassifications out of accumulated other comprehensive income, net of tax
Interest expense			229
Provision for income taxes			(87)
Net income available to common shareholders			$ 142