Fair Value of Assets and Liabilities - Schedule of Assets and Liabilities Measure at Fair Value (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Interest rate cap
Recurring Fair Value Measurements:
Fair value of assets		$ 17
Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate cap
Recurring Fair Value Measurements:
Fair value of assets		0
Significant Other Observable Inputs (Level 2) | Interest rate cap
Recurring Fair Value Measurements:
Fair value of assets		17
Significant Unobservable Inputs (Level 3) | Interest rate cap
Recurring Fair Value Measurements:
Fair value of assets		0
Marketable securities
Recurring Fair Value Measurements:
Fair value of assets	$ 249,602	276,928
Marketable securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Recurring Fair Value Measurements:
Fair value of assets	249,602	276,928
Marketable securities | Significant Other Observable Inputs (Level 2)
Recurring Fair Value Measurements:
Fair value of assets	0	0
Marketable securities | Significant Unobservable Inputs (Level 3)
Recurring Fair Value Measurements:
Fair value of assets	$ 0	$ 0