Stockholders' Deficit - Narrative (Details) - USD ($)			1 Months Ended	3 Months Ended				6 Months Ended
	Jul. 12, 2019	Apr. 05, 2019	Jan. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Feb. 20, 2019	Oct. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Dividends paid on common stock								$ 23,346,000	$ 28,757,000
Dividends declared per common share (USD per share)				$ 0.69	$ 0.69	$ 0.63	$ 0.63	$ 1.38	$ 1.26
Dividends payable				$ 12,176,000		$ 11,389,000		$ 12,176,000
Dividends paid per common share (USD per share)		$ 0.69	$ 0.63	$ 0.69			$ 0.63	$ 1.32	$ 1.60
Treasury stock reissued (shares)								187,367
Reissuance of treasury stock				$ 170,000			$ 164,000	$ 6,938,000	$ 620,000
Treasury Stock
Equity, Class of Treasury Stock [Line Items]
Treasury stock reissued (shares)				(19,000)			(26,000)	(187,000)	(103,000)
Reissuance of treasury stock				$ 822,000			$ 1,007,000	$ 8,257,000	$ 3,958,000
2019 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount										$ 200,000,000
October 2015 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount											$ 150,000,000
Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Dividends paid per common share (USD per share)	$ 0.69