Summary of Significant Accounting Policies (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investments
Minimum period considered for applying equity method accounting based on financial information provided by the investee									1 month
Maximum period considered for applying equity method accounting based on financial information provided by the investee									3 months
Accounts Receivable
Premiums receivable, allowance for doubtful accounts	$ 456				$ 635				$ 456	$ 635
Deferred Policy Acquisition Costs
Amortization expense									126,201	118,850	110,795
Premiums and Unearned Premiums
Term over which premiums are earned									1 year
Deferred revenue	15,453				15,199				15,453	15,199
Computation of basic and diluted EPS
Net income available to common shareholders for basic and diluted earnings per share	$ 11,652	$ 17,656	$ 18,059	$ 13,984	$ 9,571	$ 14,334	$ 16,956	$ 17,209	$ 61,351	$ 58,070	$ 13,702
Weighted average common and common equivalent shares outstanding used to calculate basic earnings per share									15,354,468	15,288,346	15,165,065
Common equivalent shares - stock options									5,558	7,106	10,941
Common equivalent shares- non-vested stock grants									39,775
Weighted average common and common equivalent shares outstanding used to calculate diluted earnings per share									15,399,801	15,295,452	15,176,006
Basic earnings per share (in dollars per share)	$ 0.76	$ 1.15	$ 1.17	$ 0.91	$ 0.62	$ 0.94	$ 1.11	$ 1.13	$ 4.00	$ 3.80	$ 0.90
Diluted earnings per share (in dollars per share)	$ 0.76	$ 1.14	$ 1.17	$ 0.91	$ 0.62	$ 0.94	$ 1.11	$ 1.13	$ 3.98	$ 3.80	$ 0.90
Minimum
Property, plant and equipment
Estimated useful lives									3 years
Maximum
Property, plant and equipment
Estimated useful lives									10 years