Selected Quarterly Financial and Supplementary Data - Schedule of Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gross sales	$ 175,505		$ 112,233		$ 134,487		$ 103,711		$ 178,682		$ 99,867		$ 119,054		$ 93,935		$ 525,936	$ 491,538	$ 433,856
Net revenues	182,277		112,619		134,554		105,006		177,866		99,399		118,638		94,741		534,456	490,644	433,326
Gross profit	78,871		46,889		57,502		46,825		79,167		37,602		48,557		38,899		230,087	204,225	176,965
Income from continuing operations	40,249	[1]	17,276	[1]	25,124	[1]	21,115	[1]	37,949	[2]	13,721	[2]	20,810	[2]	14,845	[2]	103,764	87,325	57,176
(Loss)/income from discontinued operations, net of tax	10	[3]	20	[3]	(94)	[3]	(1,250)	[3]	(565)	[3]	(4,503)	[3]	(316)	[3]	(263)	[3]	(1,314)	(5,647)	41
Net income	$ 40,259		$ 17,296		$ 25,030		$ 19,865		$ 37,384		$ 9,218		$ 20,494		$ 14,582		$ 102,450	$ 81,678	$ 57,217
Basic (in dollars per share)	$ 1.23	[4]	$ 0.53	[4]	$ 0.77	[4]	$ 0.61	[4]	$ 1.16	[4]	$ 0.29	[4]	$ 0.64	[4]	$ 0.46	[4]	$ 3.14	$ 2.55	$ 1.82
Diluted (in dollars per share)	$ 1.20	[4]	$ 0.52	[4]	$ 0.75	[4]	$ 0.60	[4]	$ 1.13	[4]	$ 0.28	[4]	$ 0.62	[4]	$ 0.44	[4]	$ 3.06	$ 2.48	$ 1.76
Basic (in shares)	32,810	[4]	32,749	[4]	32,629	[4]	32,454	[4]	32,240	[4]	32,149	[4]	32,063	[4]	31,886	[4]	32,662	32,086	31,420
Diluted (in shares)	33,532	[4]	33,512	[4]	33,469	[4]	33,365	[4]	33,107	[4]	32,999	[4]	32,926	[4]	32,771	[4]	33,486	32,969	32,555

[1] Income from continuing operations for the first, second, third, and fourth quarters includes a favorable impact to tax expense of $2,654, $1,725, $735, and $122, respectively, from the adoption of ASU 2016-09, and expense of $117 in the fourth quarter as a result of the change in enacted tax rates in the U.S. and the toll tax.

[2] Income from continuing operations for the first, second, third, and fourth quarters includes $290 of expense, $154 of expense, a $47 benefit and $761 of expense, respectively, for restructuring related to the decision to sell our finished dosage form facility in Hyderabad, India.

[3] Discontinued operations include charges and reimbursements for environmental remediation related to sites of divested businesses.

[4] Earnings per share calculations for each of the quarters are based on the weighted average number of shares outstanding for each period. As such, the sum of the quarters may not necessarily equal the earnings per share amount for the year.