Pro Forma Financial Information (re: 2015 and 2014 acquisitions) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition, Pro Forma Information [Abstract]
Total revenues	$ 70,204	$ 66,813	$ 64,712	$ 63,753	$ 60,633	$ 50,808	$ 51,476	$ 51,404	$ 50,847	$ 50,293	$ 51,004	$ 52,566	$ 265,482	$ 214,321	$ 204,710
Net Income, As Reported	$ 21,929	$ 20,232	$ 19,036	$ 18,336	$ 16,547	$ 18,015	$ 13,579	$ 15,417	$ 15,245	$ 13,143	$ 13,542	$ 17,344	$ 79,533	$ 63,558	$ 59,274
Basic EPS, As Reported (in dollars per share)	$ 0.65	$ 0.59	$ 0.54	$ 0.51	$ 0.45	$ 0.47	$ 0.35	$ 0.40	$ 0.40	$ 0.35	$ 0.36	$ 0.47	$ 2.29	$ 1.68	$ 1.58
Diluted EPS, As Reported (in dollars per share)	$ 0.65	$ 0.59	$ 0.54	$ 0.51	$ 0.45	$ 0.47	$ 0.35	$ 0.40	$ 0.40	$ 0.34	$ 0.35	$ 0.45	$ 2.28	$ 1.67	$ 1.53
Increase (decrease) in reported revenue													$ 51,200
Increase (decrease) in reported revenue, percentage													23.90%
Effect of Exchange Rate on Revenue													$ (10,700)	$ (3,200)	$ (3,800)
Parent, Curepet, Healthcare Magic, Vertex, Oakstone, I3, Qatarlyst
Business Acquisition, Pro Forma Information [Abstract]
Revenue, Pro forma													272,235	280,454
Net Income, Pro Forma													$ 79,412	$ 64,432
Basic EPS, Pro Forma (in dollars per share)													$ 2.29	$ 1.70
Diluted EPS, Pro Forma (in dollars per share)													$ 2.28	$ 1.69
Increase (decrease) in unaudited pro forma revenue													$ (8,200)
Increase (decrease) in unaudited pro forma revenue, percentage													2.90%
Exchange rate effect on reported revenues													$ (10,700)