Investments (Amortized Cost and Estimated Fair Value of Investments in Debt and Equity Securities by Category) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Investments, Amortized Cost	$ 439,465	$ 433,529
Investments, Gross Unrealized Gains	30,574	31,696
Investments, Gross Unrealized Losses	(4,519)	(3,900)
Investments, Fair Value	465,520	461,325
Equity Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	24,910	24,902
Investments, Gross Unrealized Gains	25,567	26,642
Investments, Gross Unrealized Losses	(490)	(314)
Investments, Fair Value	49,987	51,230
Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	414,555	408,627
Investments, Gross Unrealized Gains	5,007	5,054
Investments, Gross Unrealized Losses	(4,029)	(3,586)
Investments, Fair Value	415,533	410,095
Us Treasury Securities and Obligations of U.S. Government [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	75,390	78,894
Investments, Gross Unrealized Gains	44	24
Investments, Gross Unrealized Losses	(129)	(165)
Investments, Fair Value	75,305	78,753
Corporate Bonds [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	39,917	42,946
Investments, Gross Unrealized Gains	1,357	1,379
Investments, Gross Unrealized Losses	(437)	(450)
Investments, Fair Value	40,837	43,875
Collateralized Corporate Bank Loans [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	99,555	102,053
Investments, Gross Unrealized Gains	447	614
Investments, Gross Unrealized Losses	(857)	(489)
Investments, Fair Value	99,145	102,178
Municipal Bonds [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	159,924	156,950
Investments, Gross Unrealized Gains	2,559	2,577
Investments, Gross Unrealized Losses	(1,803)	(1,975)
Investments, Fair Value	160,680	157,552
Mortgage Backed [Member] | Debt Securities [Member]
Schedule of Investments [Line Items]
Investments, Amortized Cost	39,769	27,784
Investments, Gross Unrealized Gains	600	460
Investments, Gross Unrealized Losses	(803)	(507)
Investments, Fair Value	$ 39,566	$ 27,737