Investments - Securities and Investments, Recorded at Either Fair Value or Cost (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 350,817	$ 347,407
Gross Unrealized Gains	16,697	17,939
Gross Unrealized Losses	(561)	(300)
Available-for-sale-securities, Fair Value/Carrying Value	366,953	365,046
Restricted investment held at cost	30,000	48,250
Other investments held at cost	1,659	1,689
Total carrying value of available-for-sale investments	398,612	414,985
Deferred Compensation Plan Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,523	12,300
Gross Unrealized Gains	2,770	2,847
Gross Unrealized Losses	(16)	(24)
Available-for-sale-securities, Fair Value/Carrying Value	15,277	15,123
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	130,437	166,370
Gross Unrealized Gains	456	534
Gross Unrealized Losses	(30)	(45)
Available-for-sale-securities, Fair Value/Carrying Value	130,863	166,859
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	157,851	135,773
Gross Unrealized Gains	673	583
Gross Unrealized Losses	(137)	(54)
Available-for-sale-securities, Fair Value/Carrying Value	158,387	136,302
Municipal Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,840	8,310
Available-for-sale-securities, Fair Value/Carrying Value	24,840	8,310
Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	25,166	24,654
Gross Unrealized Gains	12,798	13,975
Gross Unrealized Losses	(378)	(177)
Available-for-sale-securities, Fair Value/Carrying Value	$ 37,586	$ 38,452