Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	$ 962,933	$ 824,868
Trading:
Fixed maturity securities	1,251	7,388
Short-term investments	50,225	131,856
Fixed maturity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	888,480	756,963
State and municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	119,853	99,046
Residential mortgage-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	136,712	115,249
Corporate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	340,422	267,882
Commercial mortgage and asset-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	136,292	113,341
Obligations of U.S. government corporations and agencies
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	95,976	101,275
U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	57,265	58,269
Redeemable preferred stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	1,960	1,901
Equity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	74,453	67,905
Recurring basis
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	962,933	824,868
Trading:
Fixed maturity securities	1,251	7,388
Short-term investments	50,225	131,856
Recurring basis | Fixed maturity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	888,480	756,963
Recurring basis | State and municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	119,853	99,046
Recurring basis | Residential mortgage-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	136,712	115,249
Recurring basis | Corporate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	340,422	267,882
Recurring basis | Commercial mortgage and asset-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	136,292	113,341
Recurring basis | Obligations of U.S. government corporations and agencies
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	95,976	101,275
Recurring basis | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	57,265	58,269
Recurring basis | Redeemable preferred stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	1,960	1,901
Recurring basis | Equity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	74,453	67,905
Recurring basis | Preferred stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	55,977	49,601
Recurring basis | Common stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	18,476	18,304
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	74,276	$ 74,461
Trading:
Fixed maturity securities	1,251
Short-term investments	25,930	$ 58,507
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Fixed maturity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	$ 56,534	$ 56,891
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | State and municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Residential mortgage-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Corporate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Commercial mortgage and asset-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Obligations of U.S. government corporations and agencies
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	$ 56,534	$ 56,891
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Redeemable preferred stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Equity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	$ 17,742	$ 17,570
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Preferred stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Common stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	$ 17,742	$ 17,570
Recurring basis | Significant Other Observable Inputs Level 2
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	$ 888,657	750,407
Trading:
Fixed maturity securities		7,388
Short-term investments	$ 24,295	73,349
Recurring basis | Significant Other Observable Inputs Level 2 | Fixed maturity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	831,946	700,072
Recurring basis | Significant Other Observable Inputs Level 2 | State and municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	119,853	99,046
Recurring basis | Significant Other Observable Inputs Level 2 | Residential mortgage-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	136,712	115,249
Recurring basis | Significant Other Observable Inputs Level 2 | Corporate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	340,422	267,882
Recurring basis | Significant Other Observable Inputs Level 2 | Commercial mortgage and asset-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	136,292	113,341
Recurring basis | Significant Other Observable Inputs Level 2 | Obligations of U.S. government corporations and agencies
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	95,976	101,275
Recurring basis | Significant Other Observable Inputs Level 2 | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	731	1,378
Recurring basis | Significant Other Observable Inputs Level 2 | Redeemable preferred stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	1,960	1,901
Recurring basis | Significant Other Observable Inputs Level 2 | Equity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	56,711	50,335
Recurring basis | Significant Other Observable Inputs Level 2 | Preferred stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	55,977	49,601
Recurring basis | Significant Other Observable Inputs Level 2 | Common stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities	$ 734	$ 734
Recurring basis | Significant Unobservable Inputs Level 3
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Trading:
Fixed maturity securities
Short-term investments
Recurring basis | Significant Unobservable Inputs Level 3 | Fixed maturity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | State and municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | Residential mortgage-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | Corporate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | Commercial mortgage and asset-backed
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | Obligations of U.S. government corporations and agencies
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | Redeemable preferred stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | Equity securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | Preferred stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities
Recurring basis | Significant Unobservable Inputs Level 3 | Common stock
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total available-for-sale securities