Property, Plant and Equipment

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property, Plant and Equipment

Property, plant and equipment consisted of the following:

($ in thousands)	Estimated Useful Lives	December 31, 2018		December 31, 2017
Land		$	6,723	$	6,418
Buildings and structures	10 - 40 years	213,657		195,540
Cable and wire	4 - 40 years	309,928		286,999
Equipment and software	2 - 17 years	791,401		730,228
Plant in service		1,321,709		1,219,185
Plant under construction		81,409		62,202
Total property, plant and equipment		1,403,118		1,281,387
Less accumulated amortization and depreciation		701,759		595,060
Property, plant and equipment, net		$	701,359	$	686,327

Depreciation expense for the years ended December 31, 2018, 2017, and 2016, was $142.1 million, $151.1 million, and 124.0 million, respectively. The Company leases fiber under indefeasible right of use agreements (IRUs). IRU's totaled $5.6 million and $5.9 million at December 31, 2018 and 2017 and were classified as capital lease agreements within property, plant and equipment.

At December 31, 2018 and 2017, the Company had unamortized capitalized software costs for software in service of $27.8 million and $28.0 million, respectively.

At December 31, 2018 and 2017, plant under construction consisted primarily of equipment and software, which was not placed into service.