Payables and Accrued Liabilities - Schedule of Exit Liability By Type of Cost (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)
Exit Liability [Roll Forward]
Balance at January 1, 2017	$ 12,866
Charges	7,969
Cash payments or other settlements	(12,625)
Balance at June 30, 2017	8,210
Total cumulative charges incurred	45,288
Total expected costs to be incurred (2)	48,973
Severance and related costs
Exit Liability [Roll Forward]
Charges	7,051
Cash payments or other settlements	(11,880)
Total cumulative charges incurred	34,057
Office closures and other costs
Exit Liability [Roll Forward]
Charges	918
Cash payments or other settlements	(745)
Total cumulative charges incurred	11,231
2015 Actions
Exit Liability [Roll Forward]
Balance at January 1, 2017	988
Charges	(28)
Cash payments or other settlements	(491)
Balance at June 30, 2017	469
Total cumulative charges incurred	13,745
Total expected costs to be incurred (2)	13,745
2015 Actions | Severance and related costs
Exit Liability [Roll Forward]
Charges	(57)
Cash payments or other settlements	(163)
Total cumulative charges incurred	7,181
2015 Actions | Office closures and other costs
Exit Liability [Roll Forward]
Charges	29
Cash payments or other settlements	(328)
Total cumulative charges incurred	6,564
2016 Actions
Exit Liability [Roll Forward]
Balance at January 1, 2017	11,878
Charges	168
Cash payments or other settlements	(10,898)
Balance at June 30, 2017	1,148
Total cumulative charges incurred	23,714
Total expected costs to be incurred (2)	23,738
2016 Actions | Severance and related costs
Exit Liability [Roll Forward]
Charges	118
Cash payments or other settlements	(10,609)
Total cumulative charges incurred	19,886
2016 Actions | Office closures and other costs
Exit Liability [Roll Forward]
Charges	50
Cash payments or other settlements	(289)
Total cumulative charges incurred	3,828
2017 Actions
Exit Liability [Roll Forward]
Balance at January 1, 2017	0
Charges	7,829
Cash payments or other settlements	(1,236)
Balance at June 30, 2017	6,593
Total cumulative charges incurred	7,829
Total expected costs to be incurred (2)	11,490
2017 Actions | Severance and related costs
Exit Liability [Roll Forward]
Charges	6,990
Cash payments or other settlements	(1,108)
Total cumulative charges incurred	6,990
2017 Actions | Office closures and other costs
Exit Liability [Roll Forward]
Charges	839
Cash payments or other settlements	(128)
Total cumulative charges incurred	$ 839