Investments Schedule of Available-for-sale Securities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 723,740		$ 833,375
Available-for-sale Securities, Gross Unrealized Gains	11,055		11,709
Available-for-sale Securities, Gross Unrealized Losses	(433)		(588)
Available-for-sale securities at fair value	734,362		844,496
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	4,218		4,603
Available-for-sale Securities, Gross Unrealized Gains	13		20
Available-for-sale Securities, Gross Unrealized Losses	(6)		(21)
Available-for-sale securities at fair value	4,225		4,602
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	285,192		378,055
Available-for-sale Securities, Gross Unrealized Gains	1,393		1,458
Available-for-sale Securities, Gross Unrealized Losses	(45)		(90)
Available-for-sale securities at fair value	286,540		379,423
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	4,978		4,953
Available-for-sale Securities, Gross Unrealized Gains	0		0
Available-for-sale Securities, Gross Unrealized Losses	(3)		(41)
Available-for-sale securities at fair value	4,975		4,912
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	171,338		196,961
Available-for-sale Securities, Gross Unrealized Gains	3,047		3,733
Available-for-sale Securities, Gross Unrealized Losses	(175)		(19)
Available-for-sale securities at fair value	174,210		200,675
Mortgage Backed Securities, Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	248,530	[1]	248,329	[1]
Available-for-sale Securities, Gross Unrealized Gains	6,490	[1]	6,403	[1]
Available-for-sale Securities, Gross Unrealized Losses	(178)	[1]	(388)	[1]
Available-for-sale securities at fair value	254,842	[1]	254,344	[1]
Other Aggregated Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	9,484		474
Available-for-sale Securities, Gross Unrealized Gains	112		95
Available-for-sale Securities, Gross Unrealized Losses	(26)		(29)
Available-for-sale securities at fair value	$ 9,570		$ 540

[1] All mortgage-backed securities are guaranteed by U.S. government agencies or Government-sponsored entities.