Maximum Potential Total of Future Payments Under Commitment Instruments (Details) $ in Thousands	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	$ 937,421
Maximum potential total of future payments under commitments	1,049,957
Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	325,676
Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	82,273
Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	998
Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	242,405
Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	650,078
Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	112,810
Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	514,851
Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	22,417
Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	74,203
Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	74,203
Balance on First Anniversary [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	954,774
Balance on First Anniversary [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	296,784
Balance on First Anniversary [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	67,871
Balance on First Anniversary [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	600
Balance on First Anniversary [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	228,313
Balance on First Anniversary [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	616,705
Balance on First Anniversary [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	111,510
Balance on First Anniversary [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	483,604
Balance on First Anniversary [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	21,591
Balance on First Anniversary [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	41,285
Balance on First Anniversary [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	41,285
More Than One And Within Three Years From Balance Sheet Date [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	80,030
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	28,892
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	14,402
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	398
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	14,092
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	33,371
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	1,300
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	31,247
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	824
More Than One And Within Three Years From Balance Sheet Date [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	17,767
More Than One And Within Three Years From Balance Sheet Date [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	17,767
More Than Three And Within Five Years From Balance Sheet Date [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	13,403
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	2
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	2
More Than Three And Within Five Years From Balance Sheet Date [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	13,401
More Than Three And Within Five Years From Balance Sheet Date [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	13,401
Beyond Five Years of Balance Sheet Date [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	1,750
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	1,750
Beyond Five Years of Balance Sheet Date [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	$ 1,750