Stockholders' Equity - Narrative (Details) - USD ($)		3 Months Ended
	Feb. 23, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Oct. 31, 2014
Equity, Class of Treasury Stock [Line Items]
Payments of dividends		$ 17,049,000		$ 16,598,000
Dividends declared per common share (USD per share)	$ 0.92	$ 0.92	$ 0.92	$ 0.875
Dividends payable		$ 17,011,000	$ 17,082,000
Treasury stock reissued (shares)		108,679
Treasury stock reissued		$ 3,900,000
October 2014 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 150,000,000
Stock repurchased during period, shares		214,545
Stock repurchased during period, value		$ 20,000,000
Cumulative amount of shares repurchased		419,032
Cumulative payments for repurchase of common stock		$ 37,500,000
Remaining authorized stock repurchases		$ 112,500,000