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Commitments and contingencies (Tables)
 12 Months Ended
Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]  
Estimates of Future Commitments
Detailed below are estimates of future commitments under these arrangements: 

Year 1
Year 2
Year 3
Year 4
Year 5
Thereafter
Total
Power purchase (i)
$
74,025

$
48,344

$
49,940

$
50,214

$
50,495

$
254,380

$
527,398

Gas supply and service agreements (ii)
91,425

66,848

51,809

33,161

28,411

97,489

369,143

Service agreements
47,695

47,211

48,529

48,827

46,548

435,093

673,903

Capital projects
41,054

17,064

65

65

65

16

58,329

Operating leases
9,573

8,974

8,298

8,361

9,718

225,047

269,971

Total
$
263,772

$
188,441

$
158,641

$
140,628

$
135,237

$
1,012,025

$
1,898,744







23.Commitments and contingencies (continued)
(b)
Commitments (continued)
(i)
Power purchase: APUC’s electric distribution facilities have commitments to purchase physical quantities of power for load serving requirements. The commitment amounts included in the table above are based on market prices as of December 31, 2017. However, the effects of purchased power unit cost adjustments are mitigated through a purchased power rate-adjustment mechanism.
(ii)
Gas supply and service agreements: APUC’s gas distribution facilities and thermal generation facilities have commitments to purchase physical quantities of natural gas under contracts for purposes of load serving requirements and of generating power.