Summary of Significant Accounting Policies - Litigation, Merger and Other Non-routine Costs, Net of Insurance Recoveries (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Litigation and other non-routine costs:
Transfer taxes	$ 0	$ (1,595,000)	$ 562,000
Audit Committee Investigation and related matters	59,755,000	49,434,000	24,207,000
Legal fees and expenses	530,000	421,000	311,000
Litigation settlements	233,246,000	0	0
Total costs	293,531,000	48,260,000	25,080,000
Insurance recoveries	(2,568,000)	(300,000)	(21,196,000)
Total	290,963,000	47,960,000	3,884,000
Reversal of accrual	(10,900,000)	$ 0	$ 0
Insurance recoveries, prior mergers	$ 2,300,000