Offsetting Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets
Net Amounts of Assets Presented in the Statement of Financial Position	$ 71,040	$ 89,361
Liabilities
Gross Amounts of Recognized Liabilities	2,718,609	2,480,181
Net Amounts of Liabilities Presented in the Statement of Financial	2,718,609	2,480,181
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments	2,718,365	2,476,768
Cash Collateral Pledged	244	3,413
Derivatives
Assets
Gross Amounts of Recognized Assets	71,040	89,361
Net Amounts of Assets Presented in the Statement of Financial Position	71,040	89,361
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments	1,323	491
Net Amount	69,717	88,870
Liabilities
Gross Amounts of Recognized Liabilities	1,567	3,904
Net Amounts of Liabilities Presented in the Statement of Financial	1,567	3,904
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments	1,323	491
Cash Collateral Pledged	244	3,413
Repurchase agreements
Liabilities
Gross Amounts of Recognized Liabilities	2,717,042	2,476,277
Net Amounts of Liabilities Presented in the Statement of Financial	2,717,042	2,476,277
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments	$ 2,717,042	$ 2,476,277