BUSINESS ACQUISITIONS - BioRx, LLC (Details) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended								12 Months Ended
	Apr. 01, 2015 USD ($) shares	Jun. 30, 2014 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Business acquisition
Net sales			$ 986,823	$ 946,913	$ 808,011	$ 624,883	$ 612,075	$ 595,529	$ 541,675	$ 465,677	$ 3,366,631	$ 2,214,956	$ 1,515,139
Summary of the preliminary fair value determination of the acquired assets and liabilities
Goodwill			256,318				23,148				256,318	23,148	$ 1,537
Definite-lived intangible assets
Contingent consideration liability							$ 5,409					5,409
Amortization expense											24,229	$ 4,030
Class B Nonvoting Common Stock
Business acquisition
Restricted common shares		$ 12,000
BioRx, LLC
Business acquisition
Cash at closing	$ 217,024
Number of shares issued | shares	4,038,853
Restricted common shares	$ 125,697
Contingent consideration at fair value	41,000
Total	$ 383,721
Market price (in dollars per share) | $ / shares						$ 34.58
Market price multiplier to factor in restricted nature of the shares (as a percent)						90
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
Purchase consideration deposited into an escrow account	$ 10,000
Deposit term into an escrow account	2 years
Acquisition-related costs charged to Selling, general, and administrative expenses											1,398
Summary of the preliminary fair value determination of the acquired assets and liabilities
Cash and cash equivalents	$ 1,786
Accounts receivable	37,716
Inventories	5,546
Deferred income taxes	715
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	(8,495)
Total identifiable net assets	192,319
Goodwill	191,402
Total acquisition price	383,721
Definite-lived intangible assets
Amount	181,700
Contingent consideration liability			$ 46,208								$ 46,208
Patient relationships | BioRx, LLC
Summary of the preliminary fair value determination of the acquired assets and liabilities
Definite-lived intangible assets	$ 130,000
Definite-lived intangible assets
Useful Life	10 years
Amount	$ 130,000
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
Definite-lived intangible assets
Useful Life	5 years
Amount	$ 39,700
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
Definite-lived intangible assets
Useful Life	8 years
Amount	$ 12,000