Available For Sale Securities (Amortized Cost And Estimated Fair Value Of Investments Classified As Available For Sale By Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Available For Sale Securities [Abstract]
Due within one year, Amortized Cost	$ 228,255
Due after one year through five years, Amortized Cost	14,776
Fixed maturities investments excluding mortgage-backed and asset-backed securities, Amortized Cost	243,031
Mortgage-backed and asset-backed securities, Amortized Cost	648,289
Total fixed maturities investments, Amortized Cost	891,320
Due within one year, Estimated Fair Value	228,292
Due after one year through five years, Estimated Fair Value	14,847
Fixed maturities investments excluding mortgage-backed and asset-backed securities, Estimated Fair Value	243,139
Mortgage-backed and asset-backed securities, Estimated Fair Value	657,298
Total fixed maturities investments, Estimated Fair Value	$ 900,437