Information Provided in Connection with Outstanding Debt of Subsidiaries - Condensed Consolidating Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013		Jun. 30, 2013	Dec. 31, 2012
Assets
Investments	$ 4,047.80	$ 4,079.20	[1]
Cash	136.2	157.4	[1]	102.0	95.8
Accrued investment income	23.5	25.7	[1]
Premiums receivable	429.2	348.4	[1]
Reinsurance recoverables	1,008.60	1,263.50	[1]
Goodwill and other intangible assets, net	237.2	239.8
Current income taxes receivable, net	8.1	0	[1]
Deferred acquisition costs, net	126.1	113.9	[1]
Ceded unearned premiums	244.3	196.3	[1]
Other assets	160.2	166.8	[1]
Due from affiliates	0	0
Intercompany note receivable	0	0
Investments in subsidiaries	0	0
Total assets	6,421.20	6,591.00	[1]
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	3,067.90	3,230.30	[1]
Unearned premiums	841.2	779.1	[1]
Funds held and ceded reinsurance payable, net	266.0	398.4
Long-term debt	403.4	403.4
Current income taxes payable, net	0	5.2	[1]
Deferred tax liabilities, net	46.3	28.7	[1]
Accrued underwriting expenses and other liabilities	163.3	182.9
Intercompany note payable	0	0
Total liabilities	4,788.10	5,028.00	[1]
Total shareholders' equity	1,633.10	1,563.00	[1]
Total liabilities and shareholders' equity	6,421.20	6,591.00	[1]
Consolidating Adjustments [Member]
Assets
Investments	0	0
Cash	0	0		0	0
Accrued investment income	0	0
Premiums receivable	0	0
Reinsurance recoverables	0	0
Goodwill and other intangible assets, net	0	0
Current income taxes receivable, net	0	0
Deferred acquisition costs, net	0	0
Ceded unearned premiums	0	0
Other assets	(6.4)	0
Due from affiliates	(5.4)	(3.1)
Intercompany note receivable	0	0
Investments in subsidiaries	(1,711.10)	(1,625.20)
Total assets	(1,722.90)	(1,628.30)
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	0	0
Unearned premiums	0	0
Funds held and ceded reinsurance payable, net	0	0
Long-term debt	0	0
Current income taxes payable, net	0	0
Deferred tax liabilities, net	0	0
Accrued underwriting expenses and other liabilities	0	0
Intercompany note payable	(33.8)	(6.6)
Total liabilities	(33.80)	(6.60)
Total shareholders' equity	(1,689.10)	(1,621.70)
Total liabilities and shareholders' equity	(1,722.90)	(1,628.30)
Argo Group International Holdings, Ltd (Parent Guarantor) [Member]
Assets
Investments	2.40	1.10
Cash	0	0		0	0
Accrued investment income	0	0
Premiums receivable	0	0
Reinsurance recoverables	0	0
Goodwill and other intangible assets, net	0	0
Current income taxes receivable, net	0	0
Deferred acquisition costs, net	0	0
Ceded unearned premiums	0	0
Other assets	12.4	4.6
Due from affiliates	5.4	3.1
Intercompany note receivable	0	0
Investments in subsidiaries	1,711.10	1,625.20
Total assets	1,731.30	1,634.00
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	0	0
Unearned premiums	0	0
Funds held and ceded reinsurance payable, net	0	0
Long-term debt	49.0	49.0
Current income taxes payable, net	0	0
Deferred tax liabilities, net	0	0
Accrued underwriting expenses and other liabilities	15.4	15.4
Intercompany note payable	33.8	6.6
Total liabilities	98.20	71.00
Total shareholders' equity	1,633.10	1,563.00
Total liabilities and shareholders' equity	1,731.30	1,634.00
Argo Group US, Inc. and Subsidiaries (Subsidiary Issuer) [Member]
Assets
Investments	2,805.60	2,785.10
Cash	101.7	132.1		83.8	73.9
Accrued investment income	18.7	19.7
Premiums receivable	158.4	150.8
Reinsurance recoverables	1,190.50	1,145.90
Goodwill and other intangible assets, net	136.5	137.4
Current income taxes receivable, net	4.9	0.5
Deferred acquisition costs, net	55.4	55.6
Ceded unearned premiums	104.2	88.2
Other assets	101.8	97.8
Due from affiliates	(1.9)	1.5
Intercompany note receivable	70.7	87.4
Investments in subsidiaries	0	0
Total assets	4,746.50	4,702.00
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	2,178.00	2,157.00
Unearned premiums	424.2	425.5
Funds held and ceded reinsurance payable, net	647.8	642.4
Long-term debt	288.9	288.9
Current income taxes payable, net	1.6	8.9
Deferred tax liabilities, net	39.2	22.8
Accrued underwriting expenses and other liabilities	91.5	98.2
Intercompany note payable	0	0
Total liabilities	3,671.20	3,643.70
Total shareholders' equity	1,075.30	1,058.30
Total liabilities and shareholders' equity	4,746.50	4,702.00
Other Subsidiaries and Eliminations [Member]
Assets
Investments	1,239.80	1,293.00
Cash	34.5	25.3		18.2	21.9
Accrued investment income	4.8	6.0
Premiums receivable	270.8	197.6
Reinsurance recoverables	(181.90)	117.60
Goodwill and other intangible assets, net	100.7	102.4
Current income taxes receivable, net	3.2	(0.5)
Deferred acquisition costs, net	70.7	58.3
Ceded unearned premiums	140.1	108.1
Other assets	52.4	64.4
Due from affiliates	1.9	(1.5)
Intercompany note receivable	(70.7)	(87.4)
Investments in subsidiaries	0	0
Total assets	1,666.30	1,883.30
Liabilities and Shareholders' Equity
Reserves for losses and loss adjustment expenses	889.90	1,073.30
Unearned premiums	417.0	353.6
Funds held and ceded reinsurance payable, net	(381.8)	(244.0)
Long-term debt	65.5	65.5
Current income taxes payable, net	(1.6)	(3.7)
Deferred tax liabilities, net	7.1	5.9
Accrued underwriting expenses and other liabilities	56.4	69.3
Intercompany note payable	0	0
Total liabilities	1,052.50	1,319.90
Total shareholders' equity	613.80	563.40
Total liabilities and shareholders' equity	$ 1,666.30	$ 1,883.30

[1] Derived from audited consolidated financial statements.