Subsequent Events - Additional Information (Detail) (USD $)	12 Months Ended				0 Months Ended					0 Months Ended
	Dec. 31, 2013	Sep. 30, 2014	Feb. 28, 2013 Class A Redeemable Common Shares [Member]	Mar. 31, 2012 Class B Redeemable Common Shares [Member]	Jan. 02, 2014 Subsequent Event [Member]	Jan. 09, 2014 Subsequent Event [Member] Institutional Preferred Shares-2012 Series [Member]	Jan. 09, 2014 Subsequent Event [Member] Institutional Preferred Shares-2013 Series [Member]	Feb. 12, 2014 Subsequent Event [Member] Class A Redeemable Common Shares [Member]	Feb. 12, 2014 Subsequent Event [Member] Class B Redeemable Common Shares [Member]	Jan. 02, 2014 Subsequent Event [Member] 2014 [Member]	Jan. 02, 2014 Subsequent Event [Member] 2018 [Member]	Jan. 02, 2014 Subsequent Event [Member] Minimum [Member]	Jan. 02, 2014 Subsequent Event [Member] Maximum [Member]	Jan. 09, 2014 The amendments approved by the shareholders [Member] Subsequent Event [Member] Institutional Preferred Shares-2012 Series [Member]
Subsequent Event [Line Items]
Common Stock Shares Authorized						100,000								120,000
Percentage Of Share Outstanding With Voting Rights							40.00%
Annual assessment on all U.S. health insurers										$ 8,000,000,000	$ 14,300,000,000
Federal Premium Tax Assessment Excemption Limit					25,000,000
Federal Premium Tax Assessment												25,000,000	50,000,000
Federal premium tax rate					50.00%
liability for the federal premium tax		$ 334,000
Tax Rate Description	The first $25 million of a health insurer's net premium written is exempt from the federal premium tax assessment. The net premium written by a health insurer from $25 million to $50 million is subject to 50% of the federal premium tax rate.
Share dividend declared			$ 32.60	$ 21.00				$ 35.77	$ 35.77