Retirement Plans - Safe Harbor plan (Details) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($)	Mar. 31, 2019	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018
Employees' savings plan
Matching contribution by the company (as a percent)						100.00%
Discretionary matching contribution		0.75				2
Expenses recognized under 401(K) plan	$ 1.7		$ 1.8	$ 4.7	$ 5.1
Minimum
Employees' savings plan
Age of employees to be eligible to participate in the defined contribution plan				21 years
Percentage of annual base compensation that participants may elect to contribute				1.00%
Maximum
Employees' savings plan
Percentage of annual base compensation that participants may elect to contribute				50.00%
Percentage of employees salary for which the company contributes a matching contribution						4.00%