Leases - ROU Asset and Lease Liability Balances (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease right-of-use assets (within other assets)	$ 37,573	$ 42,010	$ 0
Operating lease liabilities - current (within accrued expenses and other liabilities)	6,383	6,498	0
Operating lease liabilities - non-current (within other liabilities)	$ 38,340	$ 43,351	$ 0