Fair Value - Fair Value by Hierarchy (Details) (Recurring basis, USD $) | Jun. 30, 2014 | Dec. 31, 2013 |
In Thousands, unless otherwise specified |
Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Cash and cash equivalents | $59,139 | $134,211 |
Total cash and investments | 219,597 | 291,033 |
Percentage of total cash and investments (percent) | 13.70% | 18.40% |
Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Cash and cash equivalents | 0 | 0 |
Total cash and investments | 1,373,084 | 1,285,345 |
Percentage of total cash and investments (percent) | 85.90% | 81.20% |
Long-term debt | 287,800 | 272,600 |
Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Cash and cash equivalents | 0 | 0 |
Total cash and investments | 4,949 | 5,860 |
Percentage of total cash and investments (percent) | 0.30% | 0.40% |
Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Cash and cash equivalents | 59,139 | 134,211 |
Total cash and investments | 1,597,630 | 1,582,238 |
Percentage of total cash and investments (percent) | 100.00% | 100.00% |
U.S. Government | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 66,926 | 64,496 |
U.S. Government | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 121 | 171 |
U.S. Government | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
U.S. Government | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 67,047 | 64,666 |
Fixed maturities | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 66,926 | 64,496 |
Fixed maturities | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 1,373,084 | 1,283,949 |
Fixed maturities | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 4,949 | 5,860 |
Fixed maturities | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 1,444,959 | 1,354,305 |
State and Municipal | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
State and Municipal | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 510,844 | 487,111 |
State and Municipal | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
State and Municipal | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 510,844 | 487,111 |
Mortgage- Backed Securities | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Mortgage- Backed Securities | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 391,911 | 359,162 |
Mortgage- Backed Securities | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Mortgage- Backed Securities | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 391,911 | 359,162 |
Residential | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Residential | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 351,520 | 323,346 |
Residential | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Residential | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 351,520 | 323,346 |
Commercial | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Commercial | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 40,391 | 35,816 |
Commercial | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Commercial | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 40,391 | 35,816 |
Collateralized Mortgage Obligations | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | ' | 0 |
Collateralized Mortgage Obligations | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | ' | 1,291 |
Collateralized Mortgage Obligations | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | ' | 0 |
Collateralized Mortgage Obligations | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | ' | 1,291 |
Asset-Backed Securities | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Asset-Backed Securities | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 66,256 | 70,573 |
Asset-Backed Securities | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 380 | 686 |
Asset-Backed Securities | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 66,635 | 71,259 |
Corporates | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Corporates | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 403,953 | 365,642 |
Corporates | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 4,569 | 5,175 |
Corporates | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 408,522 | 370,816 |
Equity securities | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 93,332 | 91,127 |
Equity securities | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Equity securities | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Equity securities | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 93,332 | 91,127 |
Short-term investments | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 200 | 1,200 |
Short-term investments | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 1,396 |
Short-term investments | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | 0 | 0 |
Short-term investments | Estimate of Fair Value Measurement [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis | ' | ' |
Available-for-sale Securities | $200 | $2,596 |