Earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017	Sep. 30, 2016
Numerator [Abstract]
Net Income from continuing operations	$ 33,551		$ 20,388		$ 48,652	$ 30,238
Interest expense, net of tax	704		934		2,445	2,234
Amortization of debt issuance costs, net of tax	195		183		586	569
Net income (loss), adjusted from continuing operations	34,450		21,505		51,683	33,041
Net Loss from discontinued operations	0		952		0	(15,854)
Net income (loss), adjusted	$ 34,450		$ 22,457		$ 51,683	$ 17,187
Denominator [Abstract]
Weighted-average number of shares-basic (in shares)	41,222,504		40,465,423		40,989,813	40,071,730
Dilutive securities-equity awards (in shares)	1,148,857		878,390		1,003,794	658,367
Dilutive securities-convertible debt	8,096,468		8,096,500		8,096,481	8,096,500
Weighted-average number of shares-diluted (in shares)	50,467,829		49,440,313		50,090,088	48,826,597
Net income (loss) per share from continuing operations-basic (in dollars per share)	$ 0.81		$ 0.50		$ 1.19	$ 0.75
Net loss per share from discontinued operations-basic (in dollars per share)	0		0.02		0	(0.40)
Net income (loss) per share - basic (in dollars per share)	0.81		0.52		1.19	0.35
Net income (loss) from continuing operations - diluted (in dollars per share)	0.68	[1]	0.43	[1]	1.03	0.68
Net loss per share from discontinued operations-diluted (in dollars per share)	0		0.02		0	(0.32)
Net income (loss) per share - diluted (in dollars per share)	$ 0.68	[1]	$ 0.45	[1]	$ 1.03	$ 0.36
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from calculation (in shares)			400,000

[1] See "Earnings per share" for details on calculation.