Capital Stock (Details)				3 Months Ended								12 Months Ended
	Feb. 21, 2019 $ / shares	Feb. 03, 2017 USD ($) $ / shares	Jan. 02, 2017 $ / shares	Dec. 31, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2018 USD ($) registration $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Nov. 29, 2017 shares	Feb. 24, 2016 USD ($)	Dec. 31, 2015 shares	Dec. 31, 2012 USD ($) $ / shares shares
Class of Stock [Line Items]
Treasury stock issued, shares				14,102,185				14,102,185				14,102,185	14,102,185
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
Treasury stock acquired, value | $												$ 0	$ 0	$ 232,065,000
Treasury stock acquired, price per share | $ / shares														$ 36.08
Common stock dividends | $				$ 21,933,000	$ 21,929,000	$ 21,925,000	$ 21,922,000	$ 21,837,000	$ 21,834,000	$ 21,816,000	$ 21,742,000	$ 87,709,000	$ 87,229,000
Special Cash Dividend
Class of Stock [Line Items]
Dividends declared (usd per share) | $ / shares			$ 5.77									$ 0	$ 5.77	0
Common Stock, Dividends, Per Share, Cash Paid | $ / shares		$ 5.77
Warrant, Dividends, Per Share, Cash Paid | $ / shares		$ 5.77
Common stock dividends | $		$ 499,000,000											$ 499,107,000
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	1.0	$ 1.0	$ 1.00
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				101,790,837				101,429,999				101,790,837	101,429,999	100,416,000			100,015,000	78,754,269
Common Stock, Conversion Ratio												1
Common stock converted, shares issued													48
Class Of Warrant Or Right, Number of Warrants Exercised												0	97,681	163,077
Warrant exercises, shares													97,681	163,077
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
Outstanding common stock authorized for repurchase | $																$ 400,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $				$ 168,000,000								$ 168,000,000
Common Class A | Unrestricted Stock Awards
Class of Stock [Line Items]
Common stock issued, shares								10,147					10,147	16,898
Common Class B
Class of Stock [Line Items]
Common stock issued, shares				5,557				5,557				5,557	5,557	6,000			6,000	4,455,767
Common Stock, Conversion Ratio												1
Common stock conversion, shares												0	48	0
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
Preferred stock par value (usd per share) | $ / shares				$ 0.001								$ 0.001