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Fair Value Measurements (Details) - USD ($) $ in Thousands | 6 Months Ended |
--- | --- | ---
Jun. 30, 2017 | Dec. 31, 2016
Fair Value Disclosures [Abstract] |  |
State premium tax credit investments, maturity (in years) | 2 years |
Annual average discount rate (as a percent) | 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 | $ 63,929 | $ 73,530
Obligations of U.S. states and political subdivisions | 2,165,289 | 2,143,016
Corporate debt securities | 1,827,625 | 1,743,910
ABS | 21,987 | 59,565
RMBS | 202,340 | 224,209
CMBS | 307,078 | 319,817
CLOs | 112,963 | 121,175
Total debt securities | 4,701,211 | 4,685,222
Equity securities | 7,209 | 7,128
Total investment portfolio | 4,708,420 | 4,692,350
Real estate acquired | 10,271 | 11,748
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 | 13,342 | 30,690
Obligations of U.S. states and political subdivisions | 0 | 0
Corporate debt securities | 0 | 0
ABS | 0 | 0
RMBS | 0 | 0
CMBS | 0 | 0
CLOs | 0 | 0
Total debt securities | 13,342 | 30,690
Equity securities | 2,941 | 2,860
Total investment portfolio | 16,283 | 33,550
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 | 50,587 | 42,840
Obligations of U.S. states and political subdivisions | 2,164,712 | 2,142,325
Corporate debt securities | 1,827,625 | 1,743,910
ABS | 21,987 | 59,565
RMBS | 202,340 | 224,209
CMBS | 307,078 | 319,817
CLOs | 112,963 | 121,175
Total debt securities | 4,687,292 | 4,653,841
Equity securities | 0 | 0
Total investment portfolio | 4,687,292 | 4,653,841
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 | 577 | 691
Corporate debt securities | 0 | 0
ABS | 0 | 0
RMBS | 0 | 0
CMBS | 0 | 0
CLOs | 0 | 0
Total debt securities | 577 | 691
Equity securities | 4,268 | 4,268
Total investment portfolio | 4,845 | 4,959
Real estate acquired | $ 10,271 | $ 11,748

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