Summary of Significant Accounting Policies - Litigation and Other Non-Routine Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Merger Related Costs:
Transfer taxes	$ (1,595)	$ 562	$ (2,509)
Litigation and other non-routine costs:
Audit Committee Investigation and related matters	49,434	24,207	44,242
Legal fees and expenses	421	311	2,704
Other fees and expenses	0	0	632
Total costs incurred	48,260	25,080	45,069
Insurance recoveries	(300)	(21,196)	(11,441)
Total	$ 47,960	$ 3,884	$ 33,628