4. Maturities of debt securities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Maturities Of Debt Securities Details
Due in one year or less Amortized Cost	$ 173,875	$ 111,027
Due after one year through five years Amortized Cost	304,940	268,596
Due after five years through ten years Amortized Cost	761,612	572,731
Due after ten years Amortized Cost	569,197	487,783
CMBS/RMBS/ABS/CDO/CLO Amortized Cost	987,777	1,056,693
Total Amortized Cost	2,797,401	2,496,830
Due in one year or less Fair Value	174,512	111,279
Due after one year through five years Fair Value	323,357	284,081
Due after five years through ten years Fair Value	814,554	604,800
Due after ten years Fair Value	601,292	497,819
CMBS/RMBS/ABS/CDO/CLO Fair Value	999,487	1,048,413
Total Fair Value	$ 2,913,202	$ 2,546,392