Summary of Investments (Maturities) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Held-To-Maturity, Due in One Year or Less, Amortized Cost	$ 449
Held-To-Maturity, Due in One Year or Less, Fair Value	451
Available-For-Sale, Due in One Year or Less, Amortized Cost	298,828
Available-For-Sale, Due in One Year or Less, Fair Value	304,189
Trading, Due in One Year or Less, Amortized Cost	2,684
Trading, Due in One Year or Less, Fair Value	2,831
Held-To-Maturity, Due after One Year through Five Years, Amortized Cost	793
Held-To-Maturity, Due after One Year through Five Years, Fair Value	802
Available-For-Sale, Due after One Year through Five Years, Amortized Cost	996,401
Available-For-Sale, Due after One Year through Five Years, Fair Value	1,046,833
Trading, Due after One Year through Five Years, Amortized Cost	6,043
Trading, Due after One Year through Five Years, Fair Value	6,598
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	819,748
Available-For-Sale, Due after Five Years through Ten Years, Fair Value	839,103
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	299,608
Available-For-Sale,Due after Ten Years, Fair Value	287,314
Trading, Due after Ten Years, Amortized Cost	2,686
Trading, Due after Ten Years, Fair Value	3,122
Held-To-Maturity, Amortized Cost	1,477	1,655
Held-to-Maturity, Fair Value	1,449	1,681
Available-For-Sale, Amortized Cost	2,773,629	2,724,692
Available-for-Sale, Fair Value	2,961,973	2,985,205
Trading, Amortized Cost	11,413
Trading Securities, Fair Value	12,551	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	3,938
Available-For-Sale,Not Categorized by Contractual Maturity, Fair Value	4,323
Available-For-Sale, Amortized Cost	3,938	4,480
Available-for-Sale, Fair Value	4,323	4,886
Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Held-To-Maturity, Not Categorized by Contractual Maturity, Amortized Cost	230
Held-To-Maturity, Not Categorized by Contractual Maturity, Fair Value	241
Available-For-Sale, Not Categorized by Contractual Maturity, Amortized Cost	25,959
Available-For-Sale,Not Categorized by Contractual Maturity, Fair Value	26,307
Held-To-Maturity, Amortized Cost	230	256
Held-to-Maturity, Fair Value	241	271
Available-For-Sale, Amortized Cost	25,959	27,940
Available-for-Sale, Fair Value	26,307	28,807
Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Held-To-Maturity, Not Categorized by Contractual Maturity, Amortized Cost	5
Held-To-Maturity, Not Categorized by Contractual Maturity, Fair Value	5
Available-For-Sale, Not Categorized by Contractual Maturity, Amortized Cost	261,692
Available-For-Sale,Not Categorized by Contractual Maturity, Fair Value	256,747
Held-To-Maturity, Amortized Cost	5	14
Held-to-Maturity, Fair Value	5	14
Available-For-Sale, Amortized Cost	261,692	208,042
Available-for-Sale, Fair Value	256,747	214,584
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Held-To-Maturity, Amortized Cost	1,477	1,655
Held-to-Maturity, Fair Value	1,499	1,681
Available-For-Sale, Amortized Cost	2,706,174	2,657,800
Available-for-Sale, Fair Value	$ 2,764,816	$ 2,808,078