Stockholders' Equity - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Oct. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Payments of dividends	$ 17,432,000	$ 17,049,000
Dividends declared per common share (USD per share)	$ 0.97	$ 0.92	$ 0.97
Dividends payable	$ 17,490,000			$ 17,465,000
Treasury stock reissued (shares)	194,890
Treasury stock reissued	$ 7,000,000
October 2015 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 150,000,000