Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		0	1,548	61
Net Income (Loss)	$ 31,054	$ (37,060)	$ 35,929	$ 18,803
Weighted average number of common shares outstanding (for basic calculation)	20,352,000	19,821,000	20,304,000	19,153,000
Dilutive securities	1,217,000	0	1,232,000	1,159,000
Diluted (in shares)	21,569,000	19,821,000	21,536,000	20,312,000
EPS - basic	$ 1.53	$ (1.87)	$ 1.77	$ 0.98
Diluted (In dollars per share)	$ 1.44	$ (1.87)	$ 1.67	$ 0.93