Earnings Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator
Net income - basic and diluted	$ 4,306	$ 10,846	$ 5,588	$ 18,068
Denominator
Weighted average common shares outstanding - basic (in shares)	89,806	89,703	89,958	89,400
Dilutive effect of stock options and restricted stock awards (in shares)	1,900	2,823	2,082	2,730
Dilutive effect of 2021 Convertible Notes (in shares)	0	1,265	0	636
Weighted average common shares outstanding - diluted (in shares)	91,706	93,791	92,040	92,766
Net income per common share
Basic (in dollars per share)	$ 0.05	$ 0.12	$ 0.06	$ 0.20
Diluted (in dollars per share)	$ 0.05	$ 0.12	$ 0.06	$ 0.19
Stock options and restricted stock excluded from calculation of diluted earnings per share because anti-dilutive for the period (in shares)	1,707	1,173	1,710	1,412