Investment Information - Net investment income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Net investment income:
Gross investment income	$ 76,163		$ 74,337
Investment expenses	(9,169)		(8,665)
Net investment income	66,994		65,672
Fixed Maturities
Net investment income:
Gross investment income	62,449		62,006
Term loan investments
Net investment income:
Gross investment income	5,669		4,217
Equity securities (dividends)
Net investment income:
Gross investment income	2,921		1,423
Short-term investments
Net investment income:
Gross investment income	406		392
Other
Net investment income:
Gross investment income	$ 4,718	[1]	$ 6,299	[1]

[1] Includes dividends on investment funds and other items.