Business Combinations (Narrative) (Details) - USD ($) $ in Thousands			12 Months Ended
	Jan. 01, 2014	Jan. 01, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Gain on acquisition			$ 0	$ 0	$ 32,314
Eastern Insurance Holdings [Member]
Business Acquisition [Line Items]
Voting interests acquired	100.00%
Total purchase consideration	$ 205,000
Expenses related to the purchase of business				2,200	900
Revenue of aquiree since acquisition date				202,200
Earnings of acquiree since acquisition date				$ 9,100
Medmarc [Member]
Business Acquisition [Line Items]
Total purchase consideration		$ 153,700
Expenses related to the purchase of business					2,600
Gain on acquisition					$ 32,300
Business acquisition, related premium credits to eligible policyholders		$ 7,500