Summary of Investments (Maturities) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Held-To-Maturity, Due in One Year or Less, Amortized Cost	$ 570
Held-To-Maturity, Due in One Year or Less, Fair Value	572
Available-For-Sale, Due in One Year or Less, Amortized Cost	257,096
Available-For-Sale, Due in One Year or Less, Fair Value	261,686
Trading, Due in One Year or Less, Amortized Cost	1,828
Trading, Due in One Year or Less, Fair Value	1,972
Held-To-Maturity, Due after One Year through Five Years, Amortized Cost	314
Held-To-Maturity, Due after One Year through Five Years, Fair Value	319
Available-For-Sale, Due after One Year through Five Years, Amortized Cost	989,457
Available-For-Sale, Due after One Year through Five Years, Fair Value	1,039,814
Trading, Due after One Year through Five Years, Amortized Cost	3,965
Trading, Due after One Year through Five Years, Fair Value	4,918
Held-To-Maturity, Due after Five Years through Ten Years, Amortized Cost	0
Held-To-Maturity, Due after Five Years through Ten Years, Fair Value	0
Available-For-Sale, Due after Five Years through Ten Years, Amortized Cost	830,883
Available-For-Sale, Due after Five Years through Ten Years, Fair Value	844,061
Trading, Due after Five Years through Ten Years, Amortized Cost	0
Trading, Due after Five Years through Ten Years, Fair Value	0
Held-To-Maturity, Due after Ten Years, Amortized Cost	0
Held-To-Maturity, Due after Ten Years, Fair Value	0
Available-For-Sale, Due after Ten Years, Amortized Cost	324,437
Available-For-Sale, Due after Ten Years, Fair Value	308,571
Trading, Due after Ten Years, Amortized Cost	2,687
Trading, Due after Ten Years, Fair Value	3,087
Held-To-Maturity, Amortized Cost	1,102	1,655
Held-to-Maturity, Fair Value	1,120	1,681
Available-For-Sale, Amortized Cost	2,795,051	2,724,692
Available-for-Sale, Fair Value	2,977,620	2,985,205
Trading, Amortized Cost	8,480	12,645
Trading Securities, Fair Value	9,977	13,353
Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Held-To-Maturity, Not Categorized by Contractual Maturity, Amortized Cost	0
Held-To-Maturity, Not Categorized by Contractual Maturity, Fair Value	0
Available-For-Sale, Not Categorized by Contractual Maturity, Amortized Cost	3,827
Available-For-Sale, Not Categorized by Contractual Maturity, Fair Value	4,185
Available-For-Sale, Amortized Cost	3,827	4,480
Available-for-Sale, Fair Value	4,185	4,886
Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Held-To-Maturity, Not Categorized by Contractual Maturity, Amortized Cost	218
Held-To-Maturity, Not Categorized by Contractual Maturity, Fair Value	229
Available-For-Sale, Not Categorized by Contractual Maturity, Amortized Cost	23,641
Available-For-Sale, Not Categorized by Contractual Maturity, Fair Value	23,680
Held-To-Maturity, Amortized Cost	218	256
Held-to-Maturity, Fair Value	229	271
Available-For-Sale, Amortized Cost	23,641	27,940
Available-for-Sale, Fair Value	23,680	28,807
Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Held-To-Maturity, Not Categorized by Contractual Maturity, Amortized Cost	0
Held-To-Maturity, Not Categorized by Contractual Maturity, Fair Value	0
Available-For-Sale, Not Categorized by Contractual Maturity, Amortized Cost	294,759
Available-For-Sale, Not Categorized by Contractual Maturity, Fair Value	287,085
Held-To-Maturity, Amortized Cost		14
Held-to-Maturity, Fair Value		14
Available-For-Sale, Amortized Cost	294,759	208,042
Available-for-Sale, Fair Value	287,085	214,584
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Held-To-Maturity, Amortized Cost	1,102	1,655
Held-to-Maturity, Fair Value	1,120	1,681
Available-For-Sale, Amortized Cost	2,724,100	2,657,800
Available-for-Sale, Fair Value	$ 2,769,082	$ 2,808,078