Offsetting Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets
Net Amounts of Assets Presented in the Statement of Financial Position	$ 36,938	$ 45,091
Liabilities
Gross Amounts of Recognized Liabilities	3,046,977	2,660,460
Net Amounts of Liabilities Presented in the Statement of Financial	3,046,977	2,660,460
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments	3,034,592	2,655,507
Cash Collateral Pledged	12,385	4,953
Derivatives
Assets
Gross Amounts of Recognized Assets	36,938	45,091
Net Amounts of Assets Presented in the Statement of Financial Position	36,938	45,091
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments	3,817	243
Net Amount	33,121	44,848
Liabilities
Gross Amounts of Recognized Liabilities	16,202	5,196
Net Amounts of Liabilities Presented in the Statement of Financial	16,202	5,196
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments	3,817	243
Cash Collateral Pledged	12,385	4,953
Repurchase agreements
Liabilities
Gross Amounts of Recognized Liabilities	3,030,775	2,655,264
Net Amounts of Liabilities Presented in the Statement of Financial	3,030,775	2,655,264
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments	$ 3,030,775	$ 2,655,264