Equity-Based Compensation - Additional Information (Detail) (USD $)	6 Months Ended				6 Months Ended		1 Months Ended		3 Months Ended		6 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended					12 Months Ended	6 Months Ended								6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	3 Months Ended		3 Months Ended	6 Months Ended			3 Months Ended	6 Months Ended			1 Months Ended				6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014 Fifth Vesting	Jun. 30, 2014 Stock Options	Dec. 31, 2013 Stock Options	Jun. 30, 2014 Stock Options First Anniversary	Jun. 30, 2014 Stock Options Over Three Years	Jun. 30, 2014 Stock Options Minimum	Jun. 30, 2014 Stock Options Maximum	Jun. 30, 2014 SARs	Jun. 30, 2013 SARs	Jun. 30, 2014 SARs	Jun. 30, 2013 SARs	Dec. 31, 2013 SARs	Jun. 30, 2014 SARs First Anniversary	Jun. 30, 2014 SARs Over Three Years	Jun. 30, 2014 Restricted Stock	Jun. 30, 2013 Restricted Stock	Jun. 30, 2014 Restricted Stock	Jun. 30, 2013 Restricted Stock	Jun. 30, 2014 Restricted Stock Non-Management Directors (Director Plan)	Jun. 30, 2013 Restricted Stock Non-Management Directors (Director Plan)	Jun. 30, 2014 Restricted Stock ICG 2013 Performance Plan	Dec. 31, 2013 Restricted Stock ICG 2013 Performance Plan	Jun. 30, 2014 Restricted Stock ICG's Chief Executive Officer and ICG's President	Jun. 30, 2014 Restricted Stock First Vesting ICG's Employees	Jun. 30, 2014 Restricted Stock First Vesting ICG's Chief Executive Officer and ICG's President	Jun. 30, 2014 Restricted Stock Second Vesting ICG's Employees	Jun. 30, 2014 Restricted Stock Second Vesting ICG's Chief Executive Officer and ICG's President	Jun. 30, 2014 Restricted Stock Third Vesting ICG's Employees	Jun. 30, 2014 Restricted Stock Third Vesting ICG's Chief Executive Officer and ICG's President	Jun. 30, 2014 Restricted Stock Fourth Vesting ICG's Employees	Jun. 30, 2014 Restricted Stock Minimum Condition One	Dec. 31, 2013 Restricted Stock Minimum Condition One	Jun. 30, 2014 Restricted Stock Maximum Condition Two ICG 2013 Performance Plan	Dec. 31, 2013 Restricted Stock Maximum Condition Two ICG 2013 Performance Plan	Jun. 30, 2014 Restricted Stock Award	Dec. 31, 2013 Restricted Stock Award	Jun. 30, 2014 Restricted Stock Award ICG's Chief Executive Officer and ICG's President	Jun. 30, 2014 Restricted Stock Award ICG's Chief Executive Officer and ICG's President	Jun. 30, 2014 Restricted Stock Award First Vesting	Jun. 30, 2014 Restricted Stock Award Second Vesting	Jun. 30, 2013 Deferred Stock Units	Jun. 30, 2014 Deferred Stock Units	Jun. 30, 2013 Deferred Stock Units	Dec. 31, 2013 Deferred Stock Units	Apr. 30, 2014 Deferred Stock Units Before Amended Director Plan	Apr. 30, 2014 Deferred Stock Units Amended Director Plan	Apr. 30, 2014 Deferred Stock Units First Vesting Before Amended Director Plan	Apr. 30, 2014 Deferred Stock Units Second Vesting Amended Director Plan	Jun. 30, 2014 Consolidated Entities	Jun. 30, 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									914,531		914,531		1,232,808
Aggregate intrinsic value of SARs outstanding									$ 10,800,000		$ 10,800,000		$ 12,000,000
Stock options outstanding			250	250
Aggregate intrinsic value of the stock options, outstanding			100,000	100,000
Stock Awards Vesting Shares		137,500																							1,496,885	137,500	41,636	366,666	403,448	366,666	1,694,966					3,811,935	1,185,071			1,453,700	1,328,300		22,500		29,250
Stock vesting description		137,500 shares of restricted stock vest in equal installments every six months each May and November through 2015																				(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 will vest, as determined by the Compensation Committee of ICG’s Board of Directors.	(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.	as of June 30, 2014, 37,500 shares of restricted stock granted to ICG’s non-management directors vest on the one-year anniversary of the grant date	1,496,885 shares of restricted stock vest 25% each year over a four-year period	137,500 shares of restricted stock vest in equal installments each November and May through November 9, 2015	41,636 shares of restricted stock vest in equal installments every six months each March and September through 2016	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											1,453,700 shares of restricted stock vest in equal installments each February 28, 2015, 2016, 2017 and 2018	1,328,300 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																135,000		3,230,948	168,190	37,500	30,750	158,942	130,440	37,500														127,000	2,782,000			29,250	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																$ 10.52	$ 10.54	$ 12.12	$ 10.12			$ 20.33	$ 13.09																			$ 8.40	$ 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 VWAP target will instead vest on February 28, 2016, or (2) between March 1, 2015 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 VWAP target will instead vest on February 28, 2016.
Unrecognized Equity-Based Compensation	52,255,000								887,000		887,000					49,926,000		49,926,000																		41,500,000
Equity based compensation expected to be recognized remainder of year																																				8,600,000
Equity based compensation expected to be recognized in 2015																																				16,200,000
Equity based compensation expected to be recognized in 2016																																				8,100,000
Equity based compensation expected to be recognized in 2017																																				7,400,000
Equity based compensation expected to be recognized in 2018																																				$ 1,200,000
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