Balance Sheet Offsetting (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Reverse repurchase agreements
Gross Amount Recognized	$ 200,000
Net Amount Presented in the Balance Sheet	200,000
Gross Amounts Not Offset in the Balance Sheet, Securities Collateral	(200,000)
Derivatives designated as hedging instruments
Financial assets
Gross Amount Recognized	0	2,300
Financial liabilities
Gross Amount Recognized	0	100
Derivatives designated as hedging instruments | Master netting arrangements and similar agreements
Financial assets
Gross Amount Recognized		2,249
Gross Amount Offset		(83)
Net Amount Presented in the Balance Sheet		2,166
Gross Amounts Not Offset in the Balance Sheet, Securities Collateral		(1,034)
Net Amount		1,132
Financial liabilities
Gross Amount Recognized		83
Gross Amount Offset		(83)
Derivatives not designated as hedging instruments
Financial assets
Gross Amount Recognized	48,200	66,800
Financial liabilities
Gross Amount Recognized	46,900	65,900
Derivatives not designated as hedging instruments | Master netting arrangements and similar agreements
Financial assets
Gross Amount Recognized	11,498	1,920
Gross Amount Offset	(8,158)	(1,454)
Net Amount Presented in the Balance Sheet	3,340	466
Net Amount	3,340	466
Financial liabilities
Gross Amount Recognized	39,119	65,461
Gross Amount Offset	(8,158)	(1,453)
Net Amount Presented in the Balance Sheet	30,961	64,008
Gross Amounts Not Offset in the Balance Sheet, Securities Collateral	(13,909)	(48,697)
Gross Amounts Not Offset in the Balance Sheet, Cash Collateral	1,010
Net Amount	16,042	15,311
Total financial assets and total financial liabilities | Master netting arrangements and similar agreements
Financial assets
Gross Amount Recognized	211,498	4,169
Gross Amount Offset	(8,158)	(1,537)
Net Amount Presented in the Balance Sheet	203,340	2,632
Gross Amounts Not Offset in the Balance Sheet, Securities Collateral	(200,000)	(1,034)
Net Amount	3,340	1,598
Financial liabilities
Gross Amount Recognized	39,119	65,544
Gross Amount Offset	(8,158)	(1,536)
Net Amount Presented in the Balance Sheet	30,961	64,008
Gross Amounts Not Offset in the Balance Sheet, Securities Collateral	(13,909)	(48,697)
Gross Amounts Not Offset in the Balance Sheet, Cash Collateral	1,010
Net Amount	$ 16,042	$ 15,311