Acquisitions - Grace Acquisition (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				12 Months Ended			0 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 01, 2013
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Excess of purchase price over net assets acquired	$ 99.6				$ 102.3	$ 99.6	$ 0
Acquisition related costs	0.1	2.0	1.5	1.0	0	4.6	6.8
Grace Pacific Corporation
Business Acquisition [Line Items]
Percentage of voting interest acquired								100.00%
Fair value of consideration transferred								231.6
Number of shares transferred in business combination								5.4
Net of debt assumed in business combination								67.6
Equity interest issued and issuable calculation basis								199.75
Business combination percent of common stock to transfer								85.00%
Weighted average of trading prices of common stock								$ 36.7859
Number of consecutive trading days								20
Holdback amount of cash portion of the acquisition price					9.3
Cash payment to shareholders' representative to cover for transaction costs								1
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Cash consideration								35.3
Common stock issued as consideration								196.3
Fair value of consideration transferred								231.6
Cash and cash equivalents								5.7
Accounts receivable								37.1
Contracts retention								9.6
Costs and estimated earnings in excess of billings on uncompleted contracts								11.7
Inventories								42.0
Property, plant and equipment								148.6
Mineral rights								18.0
Intangible assets								4.8
All other, net								11.3
Total assets acquired								288.8
Accounts payable and accrued liabilities								26.3
Billings in excess of cost and estimated earnings on uncompleted contracts								8.1
Deferred tax liability, long-term								26.5
Long-term debt, including current portion								72.5
All other, net								8.3
Total liabilities assumed								141.7
Non-controlling interest								9.1
Excess of purchase price over net assets acquired					93.6			93.6
Acquisition related costs						4.6
Construction and natural materials revenue since acquisition	54.9
Net earnings (loss) since acquisition	1.7
Earnings (loss) attributed to noncontrolling interest since acquisition	0.5
Business Acquisition, Pro Forma Information [Abstract]
Operating revenue						539.1	454.1
Income from continuing operations, after tax						31.7	14.8
Adjustments excluded from pro forma results						6.9
Fair Value Adjustment to Purchase Price | Grace Pacific Corporation
Business Acquisition, Pro Forma Information [Abstract]
Operating revenue	(0.1)
Income from continuing operations, after tax	(1.7)
Scenario, Previously Reported | Grace Pacific Corporation
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Cash consideration								35.3
Common stock issued as consideration								196.3
Fair value of consideration transferred								231.6
Cash and cash equivalents								5.7
Accounts receivable								37.1
Contracts retention								9.6
Costs and estimated earnings in excess of billings on uncompleted contracts								11.7
Inventories								42.0
Property, plant and equipment								148.6
Mineral rights								18.0
Intangible assets								5.8
All other, net								10.4
Total assets acquired								288.9
Accounts payable and accrued liabilities								26.3
Billings in excess of cost and estimated earnings on uncompleted contracts								7.5
Deferred tax liability, long-term								27.1
Long-term debt, including current portion								72.7
All other, net								4.9
Total liabilities assumed								138.5
Non-controlling interest								9.1
Excess of purchase price over net assets acquired								90.3
Scenario, Adjustment | Grace Pacific Corporation
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Cash consideration								0
Common stock issued as consideration								0
Fair value of consideration transferred								0
Cash and cash equivalents								0
Accounts receivable								0
Contracts retention								0
Costs and estimated earnings in excess of billings on uncompleted contracts								0
Inventories								0
Property, plant and equipment								0
Mineral rights								0
Intangible assets								(1.0)
All other, net								0.9
Total assets acquired								(0.1)
Billings in excess of cost and estimated earnings on uncompleted contracts								0.6
Deferred tax liability, long-term								(0.6)
Long-term debt, including current portion								(0.2)
All other, net								3.4
Total liabilities assumed								3.2
Non-controlling interest								0
Excess of purchase price over net assets acquired								$ 3.3