Stockholders' Equity - Narrative (Details) - USD ($)		3 Months Ended
	Feb. 14, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Oct. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Payments of dividends		$ 17,453,000		$ 17,432,000
Dividends declared per common share (USD per share)	$ 0.63	$ 0.63	$ 0.97	$ 0.97
Dividends payable		$ 11,520,000	$ 17,748,000
Treasury stock reissued (shares)		76,896
Treasury stock reissued		$ 3,000,000
October 2015 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 150,000,000