Business Combinations - Pro Forma Results of Operations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition, Pro Forma Information [Abstract]
Revenues	$ 376,695	$ 385,639
Net income	$ 20,846	$ 12,845
Basic net income per share	$ 0.63	$ 0.38
Diluted net income per share	$ 0.61	$ 0.37
Shares used in computing basic net income per share	33,054	33,505
Shares used in computing diluted net income per share	33,931	34,582