Fair Value Measurements - Available-for-Sale Securities Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	$ 50,454	$ 44,829
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	296,812	230,214
Total available-for-sale securities	50,454	44,829
Total	347,266	275,043
Long-term debt	42,182
Fair Value, Measurements, Recurring [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	40,119	35,953
Fair Value, Measurements, Recurring [Member] \| Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	10,335	8,876
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury and U.S. Government Agencies [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	1,713	1,447
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	15,306	10,860
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	11,640	11,644
Fair Value, Measurements, Recurring [Member] \| State, Municipalities, and Political Subdivisions [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	10,684	11,066
Fair Value, Measurements, Recurring [Member] \| Redeemable Preferred Stock [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	776	936
Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	296,812	230,214
Total available-for-sale securities	26,016	21,255
Total	322,828	251,469
Long-term debt	42,182
Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	15,681	12,379
Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member] \| Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	10,335	8,876
Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member] \| U.S. Treasury and U.S. Government Agencies [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	545	583
Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member] \| Corporate Bonds [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	14,360	10,860
Fair Value, Measurements, Recurring [Member] \| (Level 1) [Member] \| Redeemable Preferred Stock [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	776	936
Fair Value, Measurements, Recurring [Member] \| (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	24,438	23,574
Total	24,438	23,574
Fair Value, Measurements, Recurring [Member] \| (Level 2) [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	24,438	23,574
Fair Value, Measurements, Recurring [Member] \| (Level 2) [Member] \| U.S. Treasury and U.S. Government Agencies [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	1,168	864
Fair Value, Measurements, Recurring [Member] \| (Level 2) [Member] \| Corporate Bonds [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	946
Fair Value, Measurements, Recurring [Member] \| (Level 2) [Member] \| Commercial Mortgage-Backed Securities [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	11,640	11,644
Fair Value, Measurements, Recurring [Member] \| (Level 2) [Member] \| State, Municipalities, and Political Subdivisions [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities	10,684	11,066
Fair Value, Measurements, Recurring [Member] \| (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents
Total available-for-sale securities
Total
Long-term debt
Fair Value, Measurements, Recurring [Member] \| (Level 3) [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities
Fair Value, Measurements, Recurring [Member] \| (Level 3) [Member] \| Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities
Fair Value, Measurements, Recurring [Member] \| (Level 3) [Member] \| U.S. Treasury and U.S. Government Agencies [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities
Fair Value, Measurements, Recurring [Member] \| (Level 3) [Member] \| Corporate Bonds [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities
Fair Value, Measurements, Recurring [Member] \| (Level 3) [Member] \| Commercial Mortgage-Backed Securities [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities
Fair Value, Measurements, Recurring [Member] \| (Level 3) [Member] \| State, Municipalities, and Political Subdivisions [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities
Fair Value, Measurements, Recurring [Member] \| (Level 3) [Member] \| Redeemable Preferred Stock [Member] \| Fixed-Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available-for-sale securities