Weighted Average Shares Outstanding and Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017		Jun. 30, 2016
Weighted Avg Shares Outstanding and Earnings Per Share [Line Items]
Net income (loss) allocated to common shareholders for basic calculation	$ 14,133	$ 14,199	$ (9,657)		$ 3,758
Weighted average common shares outstanding, basic	39,827	39,584	39,738		39,509
Dilutive effect of common stock options and restricted stock units	566	718	0	[1]	631
Weighted average common shares outstanding, diluted	40,393	40,302	39,738		40,140
Basic (in dollars per share)	$ 0.35	$ 0.36	$ (0.24)		$ 0.10
Diluted (in dollars per share)	$ 0.35	$ 0.35	$ (0.24)		$ 0.09
Antidilutive shares			618

[1] Due to the net loss for the six months ended June 30, 2017, restricted stock units of approximately 618,000 have been excluded from the number of shares used in calculating diluted net loss per share, as their inclusion would be antidilutive.