New Accounting Standards (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 1,181,023				$ 1,205,946				$ 1,181,023	$ 1,205,946
Increase (decrease) in results from operations	$ 6,064	$ 222	$ 2,120	$ (5,603)	$ (98,629)	$ (14,084)	$ (3,748)	$ (6,277)	$ 2,803	(122,738)	$ (69,136)
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in results from operations										$ 1,600
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings												$ 1,700