BUSINESS ACQUISITIONS (Details) $ / shares in Units, $ in Thousands					3 Months Ended			9 Months Ended
	Jun. 19, 2015 USD ($) shares	Jun. 18, 2015 $ / shares	Feb. 26, 2015 USD ($) shares	Jun. 27, 2014 USD ($) shares	Sep. 30, 2015 USD ($)	Mar. 31, 2015 $ / shares	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) segment	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Business acquisition
Number of acquisitions not treated as asset purchase for tax purposes | segment								1
Summary of the preliminary fair value determination of the acquired assets and liabilities
Goodwill					$ 253,426			$ 253,426		$ 23,148
Burman's Apothecary, LLC
Business acquisition
Cash at closing	$ 84,296
Restricted common shares	9,578
Receivable for estimated post-closing adjustment	(6,880)
Total	$ 86,994
Restricted common shares (in shares) | shares	253,036
Market price (in dollars per share) | $ / shares		$ 42.06
Market price multiplier to factor in restricted nature of the shares (as a percent)		90.00
Acquisition-related costs charged to Selling, general, and administrative expenses					532			735
Summary of the preliminary fair value determination of the acquired assets and liabilities
Accounts receivable, net	$ 17,109
Inventories	8,668
Prepaid expenses and other current assets	7,514
Property and equipment	88
Capitalized software for internal use	17,000
Definite-lived intangible assets	23,400
Accounts payable	(25,761)
Accrued expenses - compensation and benefits	(169)
Accrued expenses - other	(6)
Total identifiable net assets	47,843
Goodwill	39,151
Total acquisition price	86,994
BioRx, LLC
Business acquisition
Cash at closing			$ 217,024
Restricted common shares			125,697
Contingent consideration fair value			41,000
Total			$ 383,721
Restricted common shares (in shares) | shares			4,038,853
Market price (in dollars per share) | $ / shares						$ 34.58
Market price multiplier to factor in restricted nature of the shares (as a percent)						90.00
Number of additional restricted Company shares to be issued upon achievement of EBITDA-based metric (in shares) | shares			1,350,309
Number of principal employees whose termination will trigger maximum contingent payout			2
Acquisition-related costs charged to Selling, general, and administrative expenses					$ 40			$ 1,394
Summary of the preliminary fair value determination of the acquired assets and liabilities
Cash and cash equivalents			$ 1,786
Accounts receivable, net			38,946
Inventories			5,546
Deferred income taxes			382
Prepaid expenses and other current assets			287
Property and equipment			494
Definite-lived intangible assets			181,700
Other noncurrent assets			163
Accounts payable			(25,088)
Accrued expenses - compensation and benefits			(1,653)
Accrued expenses - other			(852)
Deferred income taxes			(9,117)
Total identifiable net assets			192,594
Goodwill			191,127
Total acquisition price			383,721
BioRx, LLC | Subsidiary
Business acquisition
Number of acquisitions not treated as asset purchase for tax purposes | segment								1
MedPro Rx, Inc.
Business acquisition
Cash at closing				$ 52,267
Restricted common shares				12,000
Contingent consideration fair value				4,270
Total				$ 68,537
Restricted common shares (in shares) | shares				716,695
Acquisition-related costs charged to Selling, general, and administrative expenses							$ 190		$ 825
Maximum payout of contingent consideration				$ 11,500
Purchase consideration deposited into an escrow account				$ 3,500
Deposit term into an escrow account				2 years
External lease term				5 years
Summary of the preliminary fair value determination of the acquired assets and liabilities
Cash and cash equivalents				$ 668
Accounts receivable, net				9,050
Inventories				3,819
Prepaid expenses and other current assets				204
Property and equipment				697
Capitalized software for internal use				25
Definite-lived intangible assets				37,099
Accounts payable				(3,638)
Accrued expenses - compensation and benefits				(157)
Accrued expenses - other				(865)
Total identifiable net assets				46,902
Goodwill				21,635
Total acquisition price				68,537
Trade names and trademarks | BioRx, LLC
Summary of the preliminary fair value determination of the acquired assets and liabilities
Definite-lived intangible assets			12,000
Trade names and trademarks | MedPro Rx, Inc.
Summary of the preliminary fair value determination of the acquired assets and liabilities
Definite-lived intangible assets				8,700
Non-compete employment agreements | Burman's Apothecary, LLC
Summary of the preliminary fair value determination of the acquired assets and liabilities
Definite-lived intangible assets	$ 5,700
Non-compete employment agreements | BioRx, LLC
Summary of the preliminary fair value determination of the acquired assets and liabilities
Definite-lived intangible assets			$ 39,700
Non-compete employment agreements | MedPro Rx, Inc.
Summary of the preliminary fair value determination of the acquired assets and liabilities
Definite-lived intangible assets				$ 4,399