Fair Value Measurements - Available-for-Sale Securities Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financial Assets:
Total fixed-maturity securities	$ 100,177	$ 112,151
Equity securities	39,097	17,649
Total available-for-sale securities	139,274	129,800
ADC Arrangement classified as real estate investment	2,652
(Level 1) [Member]
Financial Assets:
Cash and cash equivalents	304,323	293,398
Total available-for-sale securities	65,123	46,045
Total financial assets	369,446	339,443
(Level 2) [Member]
Financial Assets:
Total available-for-sale securities	74,151	83,755
Total financial assets	74,151	83,755
Financial Liabilities:
Total long-term debt	42,343	43,390
(Level 2) [Member] | Senior Notes [Member]
Financial Liabilities:
Total long-term debt	42,343	43,390
(Level 3) [Member]
Financial Assets:
ADC Arrangement classified as real estate investment	2,592
Total financial assets	2,592
Financial Liabilities:
Total long-term debt	95,462	86,630
(Level 3) [Member] | Convertible Senior Notes [Member]
Financial Liabilities:
Total long-term debt	95,462	86,630
Fixed-Maturity Securities [Member]
Financial Assets:
Total fixed-maturity securities	100,177	112,151
Fixed-Maturity Securities [Member] | (Level 1) [Member]
Financial Assets:
Total fixed-maturity securities	26,026	28,396
Fixed-Maturity Securities [Member] | (Level 1) [Member] | U.S. Treasury and U.S. Government Agencies [Member]
Financial Assets:
Total fixed-maturity securities	656	3,520
Fixed-Maturity Securities [Member] | (Level 1) [Member] | Corporate Bonds [Member]
Financial Assets:
Total fixed-maturity securities	15,880	24,476
Fixed-Maturity Securities [Member] | (Level 1) [Member] | Redeemable Preferred Stock [Member]
Financial Assets:
Total fixed-maturity securities	9,490	400
Fixed-Maturity Securities [Member] | (Level 2) [Member]
Financial Assets:
Total fixed-maturity securities	74,151	83,755
Fixed-Maturity Securities [Member] | (Level 2) [Member] | U.S. Treasury and U.S. Government Agencies [Member]
Financial Assets:
Total fixed-maturity securities	708	1,044
Fixed-Maturity Securities [Member] | (Level 2) [Member] | Corporate Bonds [Member]
Financial Assets:
Total fixed-maturity securities	999	928
Fixed-Maturity Securities [Member] | (Level 2) [Member] | Commercial Mortgage-Backed Securities [Member]
Financial Assets:
Total fixed-maturity securities	11,531	11,332
Fixed-Maturity Securities [Member] | (Level 2) [Member] | State, Municipalities, and Political Subdivisions [Member]
Financial Assets:
Total fixed-maturity securities	60,913	70,451
Equity Securities [Member] | (Level 1) [Member]
Financial Assets:
Equity securities	39,097	17,649
Fair Value, Measurements, Recurring [Member]
Financial Assets:
Cash and cash equivalents	304,323	293,398
Total available-for-sale securities	139,274	129,800
ADC Arrangement classified as real estate investment	2,592
Total financial assets	446,189	423,198
Financial Liabilities:
Total long-term debt	137,805	130,020
Fair Value, Measurements, Recurring [Member] | Senior Notes [Member]
Financial Liabilities:
Total long-term debt	42,343	43,390
Fair Value, Measurements, Recurring [Member] | Convertible Senior Notes [Member]
Financial Liabilities:
Total long-term debt	95,462	86,630
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member]
Financial Assets:
Total fixed-maturity securities	100,177	112,151
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | U.S. Treasury and U.S. Government Agencies [Member]
Financial Assets:
Total fixed-maturity securities	1,364	4,564
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | Corporate Bonds [Member]
Financial Assets:
Total fixed-maturity securities	16,879	25,404
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | Commercial Mortgage-Backed Securities [Member]
Financial Assets:
Total fixed-maturity securities	11,531	11,332
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | State, Municipalities, and Political Subdivisions [Member]
Financial Assets:
Total fixed-maturity securities	60,913	70,451
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | Redeemable Preferred Stock [Member]
Financial Assets:
Total fixed-maturity securities	9,490	400
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Financial Assets:
Equity securities	$ 39,097	$ 17,649