Summary of Significant Accounting Policies - Litigation and Other Non-Routine Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Litigation and other non-routine costs:
Audit Committee Investigation and related matters	$ 21,728	$ 12,671
Legal fees and expenses	12	204
Total costs incurred	21,740	12,875
Insurance recoveries	0	0
Total	$ 21,740	$ 12,875