Equity-Based Compensation - Additional Information. (Detail) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended	6 Months Ended		1 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended														12 Months Ended	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Stock Options	Dec. 31, 2012 Stock Options	Jun. 30, 2013 Stock Options Minimum	Jun. 30, 2013 Stock Options Maximum	Jun. 30, 2013 SARs		Jun. 30, 2013 SARs		Jun. 30, 2013 Restricted Stock	Jun. 30, 2012 Restricted Stock	Jun. 30, 2013 Restricted Stock	Jun. 30, 2012 Restricted Stock	Jun. 30, 2013 Restricted Stock ICG 2013 Performance Plan	Jun. 30, 2013 Restricted Stock Non-Management Directors (Director Plan)	Jun. 30, 2013 Restricted Stock ICG's Employees First Vesting	Jun. 30, 2013 Restricted Stock ICG's Employees Second Vesting	Jun. 30, 2013 Restricted Stock ICG's Employees Third Vesting	Jun. 30, 2013 Restricted Stock ICG's Chief Executive Officer and ICG's President	Jun. 30, 2013 Restricted Stock ICG's Chief Executive Officer and ICG's President First Vesting	Jun. 30, 2013 Restricted Stock ICG's Chief Executive Officer and ICG's President Second Vesting	Jun. 30, 2013 Restricted Stock ICG's Chief Executive Officer and ICG's President Third Vesting	Jun. 30, 2013 Restricted Stock Minimum Condition One	Jun. 30, 2013 Restricted Stock Maximum ICG 2013 Performance Plan Condition Two	Jun. 30, 2013 Restricted Stock Award	Dec. 31, 2012 Restricted Stock Award	Jun. 30, 2013 Consolidated Entities Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards vesting period			4 years		1 year	4 years			4 years								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	4,177,416	4,338,250
Aggregate intrinsic values of SARs outstanding	$ 15.2	$ 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	60,042	130,440		229,168	366,666	366,666
Stock vesting description																	53,622 shares of restricted stock vest 25% each year over a four-year period	60,042 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	130,440 shares of restricted stock vest upon the achievement of certain performance goals		229,168 shares of restricted stock vest in equal installments each November and May through November 9, 2015	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,	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%
Shares of restricted stock granted												98,223	168,190	116,973	130,440	30,750				962,500
Percentage of shares of restricted stock to vest upon achievement of performance condition															50.00%
Restricted stock awards, closing price							$ 4.44	[1]	$ 5.27	[2]	$ 10.54	$ 10.54	$ 10.12	$ 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%
Number of Shares, Granted												98,223	168,190	116,973	130,440	30,750				962,500
Restricted stock unvested																										1,237,354	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 6,999 shares of ICG’s Common Stock during the three months ended June 30, 2013.

[2] The exercise of SARs listed in this table resulted in the issuance of 44,232 shares of ICG’s Common Stock during the six months ended June 30, 2013.