Capital Stock (Details)							3 Months Ended								12 Months Ended
	Feb. 21, 2018 $ / shares	Feb. 03, 2017 USD ($) $ / shares	Jan. 02, 2017 $ / shares	Apr. 28, 2015 $ / shares shares	Apr. 09, 2015 USD ($) $ / shares	Mar. 05, 2015 $ / shares	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Dec. 31, 2017 USD ($) registration $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 28, 2014 USD ($) $ / shares shares	Nov. 29, 2017 shares	Feb. 24, 2016 USD ($)	Oct. 13, 2014 USD ($)	Dec. 31, 2012 USD ($) $ / shares shares
Class of Stock [Line Items]
Treasury stock issued, shares							14,102,185				14,102,453				14,102,185	14,102,453
Preferred stock authorized for issuance, shares							40,000,000				40,000,000				40,000,000	40,000,000
Preferred stock par value (usd per share) | $ / shares							$ 0.001				$ 0.001				$ 0.001	$ 0.001
Registration Rights Agreement, Demand Registration, Holder Rights Percentage																						5.00%
Registration Rights Agreement, Aggregate Proceeds Expected to be Received, Benchmark Amount | $																						$ 100,000,000
Registration Rights Agreement, Registration Payment Percent of Market Capitalization																						2.50%
Treasury stock acquired, shares																6,432,455.000	6,569,056	1,101,160
Treasury stock acquired, value | $															$ 0	$ 232,065,000	$ 332,339,000	$ 68,000,000
Treasury stock acquired, price per share | $ / shares																$ 36.08	$ 50.59	$ 61.58
Treasury stock placed in trades and settled in 2015, shares																		125,566
Treasury stock placed in trades and settled in 2015 | $																		$ 8,000,000
Common stock dividends | $							$ 21,837,000	$ 21,834,000	$ 21,816,000	$ 21,742,000	$ 21,612,000	$ 22,510,000	$ 22,959,000	$ 23,215,000	$ 87,229,000	$ 90,296,000
Special Cash Dividend
Class of Stock [Line Items]
Dividends declared (usd per share) | $ / shares			$ 5.77			$ 6.73									$ 5.77		$ 6.73
Warrant, Dividends, Per Share, Cash Paid | $ / shares		$ 5.77			$ 6.73
Common stock dividends | $		$ 499,000,000			$ 649,000,000										$ 499,107,000		$ 648,644,000
Common Stock, Dividends, Per Share, Cash Paid | $ / shares		$ 5.77			$ 6.73
Regular Cash Dividend
Class of Stock [Line Items]
Dividends declared (usd per share) | $ / shares							$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 1	$ 1.0	$ 0.75
Regular Cash Dividend | Subsequent Event
Class of Stock [Line Items]
Dividends declared (usd per share) | $ / shares	$ 0.25
Dividend Restriction
Class of Stock [Line Items]
Dividends declared (usd per share) | $ / shares															$ 0.25
Oaktree Group
Class of Stock [Line Items]
Number of demand registrations | registration															5
JP Morgan
Class of Stock [Line Items]
Number of demand registrations | registration															3
Angelo Gordon & Co. LP
Class of Stock [Line Items]
Number of demand registrations | registration															3
Warrant
Class of Stock [Line Items]
Warrants issued, shares							30,551								30,551							16,789,972
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares																						$ 0.001
Common Class A
Class of Stock [Line Items]
Common stock issued, shares							101,429,999				100,416,516				101,429,999	100,416,516	100,015,000	95,708,000				78,754,269
Common Stock, Conversion Ratio															1
Common stock converted, shares issued															48		2,432,478
Class Of Warrant Or Right, Number of Warrants Exercised															97,681	163,077	1,718,652
Warrant exercises, shares															97,681	163,077	1,718,645
Common stock authorized for issuance, shares							1,000,000,000				1,000,000,000				1,000,000,000	1,000,000,000
Common stock par value (usd per share) | $ / shares							$ 0.001				$ 0.001				$ 0.001	$ 0.001
Shares Available for Resale, Per Demand Registration Rights, for Selling Stockholders																			14,145,447
Shares Resold, Per Demand Registration Rights, for Selling Stockholders							7,000,000
Shares Sold During Public Offering, Including Existing Shareholders				9,240,073
Shares Issued, Price Per Share | $ / shares				$ 56.00
Outstanding common stock authorized for repurchase | $																				$ 400,000,000	$ 400,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $							$ 168,000,000								$ 168,000,000
Treasury Stock, Shares, Acquired Life to Date Under Program																	7,670,216
Common Class A | Unrestricted Stock Awards
Class of Stock [Line Items]
Common stock issued, shares							10,147				16,898				10,147	16,898	9,536
Common Class B
Class of Stock [Line Items]
Common stock issued, shares							5,557				5,605				5,557	5,605	6,000	2,438,000				4,455,767
Common Stock, Conversion Ratio															1
Common stock conversion, shares															48	0	2,432,478
Common stock authorized for issuance, shares							1,000,000,000				1,000,000,000				1,000,000,000	1,000,000,000
Common stock par value (usd per share) | $ / shares							$ 0.001				$ 0.001				$ 0.001	$ 0.001
Preferred Stock
Class of Stock [Line Items]
Preferred stock authorized for issuance, shares							40,000,000								40,000,000