Summary of Significant Accounting Policies (Details 1) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Adjustments to the financial statement Consolidated Statement of Operations
Underwriting and certain other operating costs									$ 18,450	$ 22,404	$ 6,409
Income before income taxes	12,674	9,003	4,033	11,433	9,517	5,518	4,832	7,490	37,143	27,357	44,222
Income tax expense									7,790	3,176	9,702
Net income	9,226	7,121	3,445	9,561	8,073	4,884	4,594	6,630	29,353	24,181	34,520
Basic earnings per share	$ 0.51	$ 0.39	$ 0.19	$ 0.53	$ 0.45	$ 0.27	$ 0.25	$ 0.36	$ 1.62	$ 1.32	$ 1.85
As Reported [Member]
Adjustments to the financial statement Consolidated Statement of Operations
Underwriting and certain other operating costs										22,490	6,277
Income before income taxes					9,494	5,498	4,793	7,486		27,271	44,354
Income tax expense										3,146	9,748
Net income					8,058	4,871	4,569	6,627		24,125	34,606
Basic earnings per share											$ 1.86
Adjustment [Member]
Adjustments to the financial statement Consolidated Statement of Operations
Underwriting and certain other operating costs										(86)	132
Income before income taxes										86	(132)
Income tax expense										30	(46)
Net income										56	(86)
Basic earnings per share											$ (0.01)
As Adjusted [Member]
Adjustments to the financial statement Consolidated Statement of Operations
Underwriting and certain other operating costs										22,404	6,409
Income before income taxes										27,357	44,222
Income tax expense										3,176	9,702
Net income										$ 24,181	$ 34,520
Basic earnings per share											$ 1.85