Equity-Based Compensation - Additional Information. (Detail) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended	12 Months Ended	3 Months Ended				9 Months Ended						3 Months Ended		9 Months Ended													12 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 SARs		Sep. 30, 2012 SARs		Sep. 30, 2013 SARs		Sep. 30, 2012 SARs		Sep. 30, 2013 Stock Options	Dec. 31, 2012 Stock Options	Sep. 30, 2013 Restricted Stock	Sep. 30, 2012 Restricted Stock	Sep. 30, 2013 Restricted Stock	Sep. 30, 2012 Restricted Stock	Sep. 30, 2013 Restricted Stock ICG 2013 Performance Plan	Sep. 30, 2013 Restricted Stock Non-Management Directors (Director Plan)	Sep. 30, 2012 Restricted Stock Non-Management Directors (Director Plan)	Sep. 30, 2013 Restricted Stock ICG's Chief Executive Officer and ICG's President	Sep. 30, 2013 Restricted Stock First Vesting ICG's Employees	Sep. 30, 2013 Restricted Stock First Vesting ICG's Chief Executive Officer and ICG's President	Sep. 30, 2013 Restricted Stock Second Vesting ICG's Employees	Sep. 30, 2013 Restricted Stock Second Vesting ICG's Chief Executive Officer and ICG's President	Sep. 30, 2013 Restricted Stock Third Vesting ICG's Employees	Sep. 30, 2013 Restricted Stock Third Vesting ICG's Chief Executive Officer and ICG's President	Sep. 30, 2013 Restricted Stock Award	Dec. 31, 2012 Restricted Stock Award	Sep. 30, 2013 Minimum Stock Options	Sep. 30, 2013 Minimum Restricted Stock Condition One	Sep. 30, 2013 Maximum Stock Options	Sep. 30, 2013 Maximum Restricted Stock Condition Two ICG 2013 Performance Plan	Sep. 30, 2013 Consolidated Entities Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards vesting period							4 years				4 years										4 years								1 year		4 years		4 years
Expiry period of incentive or non-qualified stock options granted from date of grant																													8 years		10 years
SARs vesting on the first anniversary	25.00%
Remaining SARs vesting equally each month	75.00%
Subsequent vesting of remaining SARs, period	36 months
SARs outstanding	3,956,542	4,338,250
Aggregate intrinsic values of SARs outstanding	$ 25.2	$ 16.0
Equity-based compensation awards vesting on the first anniversary											25.00%																						25.00%
Remaining Equity-based compensation awards vesting equally each month											75.00%																						75.00%
Remaining awards vesting period											36 months																						36 months
Stock options, outstanding											1,750	1,750
Aggregate intrinsic value of the stock options, outstanding											$ 0.1	$ 0.1
Stock Awards Vesting Shares																					53,622	229,168	51,466	366,666	130,440	366,666
Stock vesting description																					53,622 shares of restricted stock vest 25% each year over a four-year period	229,168 shares of restricted stock vest in equal installments each November and May through November 9, 2015	51,466 shares of restricted stock vest 12.5% on the nine-month anniversary of the grant date, and the remaining 87.5% every six months subsequent to the first vesting date	366,666 shares of restricted stock vest based on the achievement of stipulated performance goals related to ICG’s results on or before December 31, 2015	130,440 shares of restricted stock vest upon the achievement of certain performance goals	366,666 shares of restricted stock vest based on stipulated market thresholds related to ICG’s Common Stock price through December 31, 2015.
Stock awards vesting rate																					25.00%
Stock awards vesting on the Nine month anniversary																							12.50%
Remaining Restricted stock awards vesting equally each six months																							87.50%
Number of Shares, Granted															168,190	116,973	130,440	30,750	18,750	962,500
Percentage of shares of restricted stock to vest upon achievement of performance condition																	50.00%
Restricted stock awards, closing price			$ 4.55	[1]	$ 4.96	[1]	$ 7.46	[2]	$ 4.96	[2]			$ 9.25		$ 10.69	$ 10.19	$ 13.09
Performance shares vesting conditions																	(1) is greater than or equal to 50%, all of that employee’s Performance Shares will vest or (2) is greater than 0% but less than 50%, a portion of that employee’s Performance Shares equal to two times the achievement percentage will vest.
Percentage of financial targets to be achieved for participants to receive award																														50.00%		50.00%
Restricted stock awards vesting on anniversary																		100.00%
Restricted stock unvested																											1,228,778	1,217,463
Deferred Stock Units unvested	29,250	41,250
Remaining awards vesting percentage on each anniversary																																	25.00%

[1] The exercise of SARs listed in this table resulted in the issuance of 55,619 shares of ICG’s Common Stock during the three months ended September 30, 2013.

[2] The exercise of SARs listed in this table resulted in the issuance of 99,851 shares of ICG’s Common Stock during the nine months ended September 30, 2013.