RESERVES FOR LOSS AND LOSS SETTLEMENT EXPENSES (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross liability for losses and loss settlement expenses at beginning of year	$ 971,911	$ 945,051	$ 603,090
Ceded loss and loss settlement expenses	75,150	103,870	120,359	39,000
Net liability for losses and loss settlement expenses at beginning of year	868,041	824,692	564,090
Reserves acquired in Mercer Insurance Group acquisition, net	0	0	252,598
Beginning balance, as adjusted	868,041	824,692	816,688
Losses and loss settlement expenses incurred for claims occurring during
Current year	494,841	512,564	468,926
Prior years	(57,487)	(73,427)	(61,095)
Total incurred	437,354	439,137	407,831
Losses and loss settlement expenses incurred for claims occurring during
Current year	203,868	201,632	253,175
Prior years	216,026	194,156	146,653
Total paid	419,894	395,788	399,828
Net liability for losses and loss settlement expenses at end of year	885,501	868,041	824,692
Ceded loss and loss settlement expenses	(75,150)	(103,870)	(120,359)	(39,000)
Gross liability for losses and loss settlement expenses at end of year	$ 960,651	$ 971,911	$ 945,051