Stockholders' Equity - Narrative (Details) - USD ($)		3 Months Ended		6 Months Ended
	Feb. 24, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Oct. 31, 2014
Equity [Abstract]
Payments of dividends				$ 33,271,000	$ 28,518,000
Dividends declared per common share (USD per share)	$ 0.875	$ 0.875	$ 0.75	$ 1.75	$ 1.5
Dividends payable		$ 16,546,000		$ 16,546,000		$ 16,635,000
Equity, Class of Treasury Stock [Line Items]
Treasury stock reissued (shares)				292,648
Treasury stock reissued				$ 10,600,000
October 2014 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount							$ 100,000,000
Stock repurchased during period, shares				344,890
Stock repurchased during period, value				$ 35,000,000
Cumulative amount of shares repurchased		365,225		365,225
Cumulative payments for repurchase of common stock		$ 37,000,000		$ 37,000,000
Remaining authorized stock repurchases		$ 63,000,000		$ 63,000,000