Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share, Basic, Two Class Method [Abstract]
Net income (loss) attributable to Granite, Earnings per share, Basic	$ 17,987	$ 37,121	$ 1,949	$ (11,773)	$ 18,754	$ 36,468	$ 4,946	$ (9,007)	$ 45,283	$ 51,161	$ (58,983)
Less: net income allocated to participating securities									283	738	0
Net income (loss) allocated to common shareholders for basic calculation									45,000	50,423	(58,983)
Weighted average common stock outstanding, basic (in shares)									38,447	38,117	37,820
Net income (loss) per share, basic (in dollars per share)	$ 0.46	$ 0.96	$ 0.05	$ (0.31)	$ 0.48	$ 0.94	$ 0.13	$ (0.24)	$ 1.17	$ 1.32	$ (1.56)
Earnings Per Share, Diluted, Two Class Method [Abstract]
Net income (loss) attributable to Grainte, Earnings per share, Diluted	17,987	37,121	1,949	(11,773)	18,754	36,468	4,946	(9,007)	45,283	51,161	(58,983)
Less: net income allocated to participating securities									279	732	0
Net income (loss) allocated to common shareholders for diluted calculation									$ 45,004	$ 50,429	$ (58,983)
Weighted average common shares outstanding, diluted (in shares)									39,076	38,473	37,820
Net income (loss) per share, diluted (in dollars per share)	$ 0.46	$ 0.94	$ 0.05	$ (0.31)	$ 0.48	$ 0.93	$ 0.13	$ (0.24)	$ 1.15	$ 1.31	$ (1.56)