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Fair Value Measurements (Details) - USD ($) $ in Thousands | 9 Months Ended |
--- | --- | ---
Sep. 30, 2016 | Dec. 31, 2015
Fair Value Disclosures [Abstract] |  |
State premium tax credit investments, average maturity | 3 years |
Annual average discount rate (in hundredths) | 7.10% |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
U.S. Treasury securities and obligations of U.S. government corporations and agencies | $ 42,256 | $ 160,584
Obligations of U.S. states and political subdivisions | 2,132,669 | 1,792,527
Corporate debt securities | 1,749,869 | 2,004,763
Asset-backed securities | 79,182 | 116,617
Residential mortgage-backed securities | 243,436 | 257,648
Commercial mortgage-backed securities | 350,213 | 233,491
Collateralized loan obligations | 121,000 | 60,200
Debt securities issued by foreign sovereign governments |  | 31,731
Total debt securities | 4,718,625 | 4,657,561
Equity securities | 7,218 | 5,645
Total investment portfolio | 4,725,843 | 4,663,206
Real estate acquired | 10,564 | 12,149
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
U.S. Treasury securities and obligations of U.S. government corporations and agencies | 8,755 | 46,197
Obligations of U.S. states and political subdivisions | 0 | 0
Corporate debt securities | 0 | 0
Asset-backed securities | 0 | 0
Residential mortgage-backed securities | 0 | 0
Commercial mortgage-backed securities | 0 | 0
Collateralized loan obligations | 0 | 0
Debt securities issued by foreign sovereign governments |  | 31,731
Total debt securities | 8,755 | 77,928
Equity securities | 2,950 | 2,790
Total investment portfolio | 11,705 | 80,718
Real estate acquired | 0 | 0
Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
U.S. Treasury securities and obligations of U.S. government corporations and agencies | 33,501 | 114,387
Obligations of U.S. states and political subdivisions | 2,131,839 | 1,791,299
Corporate debt securities | 1,749,869 | 2,004,763
Asset-backed securities | 79,182 | 116,617
Residential mortgage-backed securities | 243,436 | 257,648
Commercial mortgage-backed securities | 350,213 | 233,491
Collateralized loan obligations | 121,000 | 60,200
Debt securities issued by foreign sovereign governments |  | 0
Total debt securities | 4,709,040 | 4,578,405
Equity securities | 0 | 0
Total investment portfolio | 4,709,040 | 4,578,405
Real estate acquired | 0 | 0
Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
U.S. Treasury securities and obligations of U.S. government corporations and agencies | 0 | 0
Obligations of U.S. states and political subdivisions | 830 | 1,228
Corporate debt securities | 0 | 0
Asset-backed securities | 0 | 0
Residential mortgage-backed securities | 0 | 0
Commercial mortgage-backed securities | 0 | 0
Collateralized loan obligations | 0 | 0
Debt securities issued by foreign sovereign governments |  | 0
Total debt securities | 830 | 1,228
Equity securities | 4,268 | 2,855
Total investment portfolio | 5,098 | 4,083
Real estate acquired | $ 10,564 | $ 12,149

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