Schedule I - Summary of Investments-Other than Investments in Related Parties (Details) (USD $)	Dec. 31, 2013
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 1,181,965,334
Fair value	1,256,389,808
Amount at which shown in the balance sheet	1,256,389,808
Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,009,572,325
Fair value	1,027,984,013
Amount at which shown in the balance sheet	1,027,984,013
US Treasury Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	9,539,657
Fair value	9,412,497
Amount at which shown in the balance sheet	9,412,497
US Government-sponsored Enterprises Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	156,980,739
Fair value	146,945,719
Amount at which shown in the balance sheet	146,945,719
Obligations of States and Political Subdivisions [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	346,554,566
Fair value	357,051,689
Amount at which shown in the balance sheet	357,051,689
Commercial Mortgage Backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	63,184,992
Fair value	68,939,577
Amount at which shown in the balance sheet	68,939,577
Residential Mortgage Backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	96,058,330
Fair value	94,179,189
Amount at which shown in the balance sheet	94,179,189
Other Asset Backed [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	11,455,608
Fair value	12,647,636
Amount at which shown in the balance sheet	12,647,636
Corporate Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	325,798,433
Fair value	338,807,706
Amount at which shown in the balance sheet	338,807,706
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	113,835,488
Fair value	169,848,274
Amount at which shown in the balance sheet	169,848,274
Common stocks Financial services [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	19,272,973
Fair value	28,498,329
Amount at which shown in the balance sheet	28,498,329
Common stocks Information technology [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	12,644,716
Fair value	18,917,368
Amount at which shown in the balance sheet	18,917,368
Common stocks Healthcare [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	12,801,287
Fair value	21,944,614
Amount at which shown in the balance sheet	21,944,614
Common stocks Consumer staples [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	9,162,313
Fair value	13,010,682
Amount at which shown in the balance sheet	13,010,682
Common stocks Consumer discretionary [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	10,722,050
Fair value	21,031,295
Amount at which shown in the balance sheet	21,031,295
Common stocks Energy [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	14,102,214
Fair value	21,117,265
Amount at which shown in the balance sheet	21,117,265
Common stocks Industrials [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	11,189,958
Fair value	17,264,144
Amount at which shown in the balance sheet	17,264,144
Common stocks Other [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	13,357,539
Fair value	17,811,177
Amount at which shown in the balance sheet	17,811,177
Nonredeemable Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	10,582,438
Fair value	10,253,400
Amount at which shown in the balance sheet	10,253,400
Other Long-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,391,987
Fair value	2,391,987
Amount at which shown in the balance sheet	2,391,987
Short-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	56,165,534
Fair value	56,165,534
Amount at which shown in the balance sheet	$ 56,165,534