Investments (Components of net investment income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net investment income
Net investment income	$ 31,612	$ 31,572	$ 33,611	$ 31,029	$ 30,169	$ 25,265	$ 21,286	$ 23,366	$ 127,824	$ 100,086	$ 96,089
Managed investments
Net investment income
Total gross investment income									128,861	103,272	100,070
Investment expenses									(7,695)	(7,472)	(7,863)
Net investment income									121,166	95,800	92,207
Managed investments | Fixed Maturities And Short Term Investments [Member]
Net investment income
Total gross investment income									113,627	93,044	95,386
Managed investments | Other investments [Member]
Net investment income
Total gross investment income									13,307	5,111	0
Managed investments | Cash and cash equivalents
Net investment income
Total gross investment income									1,911	5,106	4,678
Managed investments | Securities lending income
Net investment income
Total gross investment income									16	11	6
Non-managed investments
Net investment income
Net investment income									6,658	4,286	3,882
Non-managed investments | Fixed Maturities And Short Term Investments [Member]
Net investment income
Total gross investment income									6,528	4,204	3,847
Non-managed investments | Restricted cash and cash and cash equivalents
Net investment income
Total gross investment income									$ 130	$ 82	$ 35