Weighted Average Shares Outstanding and Net Income Per Share - Summary of Reconciliation of Weighted Average Shares Outstanding in Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income allocated to common shareholders for basic calculation		$ 55,672	$ 45,982	$ 35,864	$ 36,325
Effect of dilutive convertible notes		296	0	0	0
Net income allocated to common shareholders for diluted calculation		$ 55,968	$ 45,982	$ 35,864	$ 36,325
Weighted average common shares outstanding, basic		46,308	39,844	42,443	39,774
Dilutive effect of convertible notes, restricted stock units and common stock options	[1]	1,502	543	467	593
Weighted average common shares outstanding, diluted		47,810	40,387	42,910	40,367
Net income per share, basic		$ 1.20	$ 1.15	$ 0.84	$ 0.91
Net income per share, diluted		$ 1.17	$ 1.14	$ 0.84	$ 0.90

[1] 1Weighted average shares of approximately 1.1 million have been included in the number of shares used in calculating diluted net income per share for the three months ended September 30, 2018 based on the assumption that the 8% Convertible Notes were converted to Granite shares as of July 1, 2018 through their conversion on August 15, 2018. The shares have been excluded from the nine months ended September 30, 2018 as their inclusion would be antidilutive. See Note 14 for further discussion on the 8% Convertible Notes