Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator for calculation of diluted earnings per share
Net income	$ 8,873	$ 91,069	$ (48,704)	$ 73,295
Denominator for diluted income per share
Weighted-average shares outstanding	61,074	60,850	61,013	60,803
Dilutive effect of stock equivalents (in shares)	277	283	0	394
Denominator for diluted earnings per share (in shares)	61,351	61,133	61,013	61,197
Diluted earnings per share (in dollars per share)	$ 0.14	$ 1.49	$ (0.8)	$ 1.2
Stock Compensation Plan [Member]
Anti-dilutive securities excluded from diluted earnings (loss) per share calculation
Anti-dilutive stock equivalents	2,165	1,036	2,071	888