Writedowns and Other Charges - Activity in Liability Account Related to Office Space Consolidation (Details) - Office Space Consolidation - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Restructuring Reserve [Roll Forward]
Balance as of beginning of period	$ 18,892	$ 5,897
Real estate charges incurred	390	23,186
Payments made, net	(3,750)	(8,921)
Interest accretion	(1,281)	(1,270)
Balance as of end of period	$ 14,251	$ 18,892