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
Earnings (numerator)
Net income attributable to common stockholders	$ 2,837	$ 19,427	$ 29,047	$ 47,014
Shares (denominator)
Weighted average common shares outstanding (basic)	48,586	47,548	48,114	47,047
Dilutive effect of stock options and stock awards outstanding	978	1,188	1,237	1,338
Adjusted weighted average common shares outstanding (diluted)	49,564	48,736	49,351	48,385
Earnings per share attributable to common stockholders
Basic	$ 0.06	$ 0.41	$ 0.60	$ 1.00
Diluted	$ 0.06	$ 0.40	$ 0.59	$ 0.97