Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Property and equipment

Depreciation of property and equipment is provided on the straight‑line method over the following estimated useful lives:

Vehicles	1 ‑ 5 years
Equipment	2 ‑ 20 years
Leasehold improvements	5 ‑ 20 years

Property and equipment consisted of the following at December 31, 2016 and 2015, respectively:

	2016		2015
Equipment and vehicles	$	402,640,458	$	399,084,240
Leasehold improvements	4,500,406		5,003,838
Subtotal	407,140,864		404,088,078
Less accumulated depreciation	143,279,219		112,249,580
Property and equipment — net	$	263,861,645	$	291,838,498