Equity-Based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			3 Months Ended		1 Months Ended		3 Months Ended		3 Months Ended							12 Months Ended	3 Months Ended							3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended			3 Months Ended						1 Months Ended				3 Months Ended
	Mar. 31, 2014	Mar. 31, 2014 Stock Options	Dec. 31, 2013 Stock Options	Mar. 31, 2014 Stock Options First Anniversary	Mar. 31, 2014 Stock Options Over Three Years	Mar. 31, 2014 Stock Options Minimum	Mar. 31, 2014 Stock Options Maximum	Mar. 31, 2014 SARs	Dec. 31, 2013 SARs	Mar. 31, 2014 SARs First Anniversary	Mar. 31, 2014 SARs Over Three Years	Mar. 31, 2014 Restricted Stock	Mar. 31, 2013 Restricted Stock	Mar. 31, 2014 Restricted Stock Non-Management Directors (Director Plan)	Mar. 31, 2013 Restricted Stock Non-Management Directors (Director Plan)	Mar. 31, 2014 Restricted Stock ICG 2013 Performance Plan	Dec. 31, 2013 Restricted Stock ICG 2013 Performance Plan	Mar. 31, 2014 Restricted Stock Chief Executive Officer	Mar. 31, 2014 Restricted Stock First Vesting ICG's Employees	Mar. 31, 2014 Restricted Stock First Vesting ICG's Chief Executive Officer and ICG's President	Mar. 31, 2014 Restricted Stock Second Vesting ICG's Employees	Mar. 31, 2014 Restricted Stock Second Vesting ICG's Chief Executive Officer and ICG's President	Mar. 31, 2014 Restricted Stock Third Vesting ICG's Employees	Mar. 31, 2014 Restricted Stock Third Vesting ICG's Chief Executive Officer and ICG's President	Mar. 31, 2014 Restricted Stock Minimum Condition One	Dec. 31, 2013 Restricted Stock Minimum Condition One	Mar. 31, 2014 Restricted Stock Maximum Condition Two ICG 2013 Performance Plan	Dec. 31, 2013 Restricted Stock Maximum Condition Two ICG 2013 Performance Plan	Mar. 31, 2014 Restricted Stock Award	Dec. 31, 2013 Restricted Stock Award	Mar. 31, 2014 Restricted Stock Award ICG's Chief Executive Officer and ICG's President	Mar. 31, 2014 Restricted Stock Award First Vesting	Mar. 31, 2014 Restricted Stock Award Second Vesting	Mar. 31, 2014 Deferred Stock Units	Mar. 31, 2013 Deferred Stock Units	Dec. 31, 2013 Deferred Stock Units	Apr. 30, 2014 Deferred Stock Units Before Amended Director Plan Subsequent Event	Apr. 30, 2014 Deferred Stock Units Amended Direrctor Plan Subsequent Event	Apr. 30, 2014 Deferred Stock Units First Vesting Before Amended Director Plan Subsequent Event	Apr. 30, 2014 Deferred Stock Units Second Vesting Amended Direrctor Plan Subsequent Event	Mar. 31, 2014 Consolidated Entities	Mar. 31, 2014 Consolidated Entities Each Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards vesting period		4 years			36 months	1 year	4 years	4 years			36 months																														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%	75.00%					25.00%	75.00%																															25.00%
SARs outstanding								938,883	1,232,808
Aggregate intrinsic value of SARs outstanding								$ 10.6	$ 12.0
Stock options outstanding		250	250
Aggregate intrinsic value of the stock options, outstanding		$ 0.1	$ 0.1
Stock Awards Vesting Shares																			50,998	183,334	41,636	366,666	403,448	366,666					3,738,582	1,185,071		1,377,500	1,277,500	22,500		29,250
Stock vesting description																(1) is greater than or equal to 100%, all of that employee’s 2014 Performance Shares will vest or (2) is greater than 0% but less than 100%, a portion of that employee’s 2014 Performance Shares equal to two times the achievement percentage will vest.	(1) was greater than or equal to 50%, all of that employee’s 2013 Performance Shares vested or (2) was greater than 0% but less than 50%, a portion of that employee’s 2013 Performance Shares equal to two times the achievement percentage vested.		50,998 shares of restricted stock vest 25% each year over a four-year period	183,334 shares of restricted stock vest in equal installments each November and May through November 9, 2015	41,636 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 stipulated market thresholds related to ICG’s Common Stock price through December 31, 2015	403,448 shares of restricted stock vest upon the achievement of certain performance goals									1,377,500 shares of restricted stock vest in equal installments each February 28, 2015, 2016, 2017 and 2018	1,277,500 shares of restricted stock vest based on stipulated market thresholds related to ICG’s Common stock price through February 28, 2018
Number of Shares, Granted												3,095,948	168,190	37,500	30,750	158,942	130,440	3,205,000													2,655,000			22,500	29,250
Percentage of shares of restricted stock to vest upon achievement of performance condition																100.00%	50.00%
Restricted stock awards, closing price												$ 12.68	$ 9.76			$ 20.33	$ 13.09																	$ 13.09	$ 8.40
Percentage of financial targets to be achieved for participants to receive award																									100.00%	50.00%	100.00%	50.00%
Volume weighted average price targets	28.07, $30.16, $32.38 and $34.71
VWAP price target declaration	(1) on or prior to February 28, 2015, 50% of the shares that would have vested upon achieving the VWAP target will instead vest on the one-year anniversary of the grant, and the remaining 50% of the shares that would have vested upon achieving the WVAP target will instead vest on February 28, 2016, or (2) between the one-year anniversary of the grant and February 28, 2016, 50% of the applicable shares will vest on the date of achievement of the VWAP target, and the remaining 50% of the shares that would have vested upon achieving the WVAP target will instead vest on February 28, 2016.
Change of non-management director service grant shares																																					7,500	22,500
Director restricted stock to be vested																																							7,500	15,000
Equity-based compensation awards vesting on the first anniversary																																									25.00%
Remaining Equity-based compensation awards vesting equally each month																																									75.00%
Remaining awards vesting period																																									36 months