CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Class A Common Stock Common Stock	Preferred Stock	Paid-in Capital	Retained Earnings	Total
Balance at Dec. 31, 2017	$ 1,036		$ 2,260,064	$ 1,866,342	$ 4,127,442
Balance (in shares) at Dec. 31, 2017	103,621,629
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon vesting of restricted stock units and upon exercise of options	$ 4		2,632		2,636
Issuance of common stock upon vesting of restricted stock units and upon exercise of options (in shares)	514,773
Stock-based compensation			3,432		3,432
Cash dividends (declared $0.10 and $0.13 per share of Class A common stock)				(10,397)	(10,397)
Tax withholding related to vesting of restricted stock units and exercise of stock options			(7,141)		(7,141)
Tax withholding related to vesting of restricted stock units and exercise of stock options (in shares)	(156,568)
Net income				110,651	110,651
Balance at Mar. 31, 2018	$ 1,040		2,258,987	1,966,596	4,226,623
Balance (in shares) at Mar. 31, 2018	103,979,834
Balance at Dec. 31, 2017	$ 1,036		2,260,064	1,866,342	4,127,442
Balance (in shares) at Dec. 31, 2017	103,621,629
Increase (Decrease) in Shareholders' Equity
Net income					372,436
Balance at Sep. 30, 2018	$ 1,041		2,270,302	2,207,575	4,478,918
Balance (in shares) at Sep. 30, 2018	104,068,079
Balance at Mar. 31, 2018	$ 1,040		2,258,987	1,966,596	4,226,623
Balance (in shares) at Mar. 31, 2018	103,979,834
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon vesting of restricted stock units and upon exercise of options	$ 1		1,521		1,522
Issuance of common stock upon vesting of restricted stock units and upon exercise of options (in shares)	85,211
Stock-based compensation			4,885		4,885
Cash dividends (declared $0.10 and $0.13 per share of Class A common stock)				(10,399)	(10,399)
Net income				115,211	115,211
Balance at Jun. 30, 2018	$ 1,041		2,265,393	2,071,408	4,337,842
Balance (in shares) at Jun. 30, 2018	104,065,045
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon vesting of restricted stock units and upon exercise of options			61		61
Issuance of common stock upon vesting of restricted stock units and upon exercise of options (in shares)	3,034
Stock-based compensation			4,848		4,848
Cash dividends (declared $0.10 and $0.13 per share of Class A common stock)				(10,407)	(10,407)
Net income				146,574	146,574
Balance at Sep. 30, 2018	$ 1,041		2,270,302	2,207,575	4,478,918
Balance (in shares) at Sep. 30, 2018	104,068,079
Balance at Dec. 31, 2018	$ 1,110		2,474,238	2,331,552	4,806,900
Balance (in shares) at Dec. 31, 2018	110,949,850
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon vesting of restricted stock units and upon exercise of options	$ 2		439		441
Issuance of common stock upon vesting of restricted stock units and upon exercise of options (in shares)	263,218
Issuance of preferred stock		$ 100	242,141		242,241
Issuance of preferred stock (in shares)		10,000,000
Stock-based compensation			4,174		4,174
Cash dividends (declared $0.10 and $0.13 per share of Class A common stock)				(14,445)	(14,445)
Tax withholding related to vesting of restricted stock units and exercise of stock options	$ (1)		(3,587)		(3,588)
Tax withholding related to vesting of restricted stock units and exercise of stock options (in shares)	(94,899)
Net income				138,094	138,094
Balance at Mar. 31, 2019	$ 1,111	$ 100	2,717,405	2,455,201	5,173,817
Balance (in shares) at Mar. 31, 2019	111,118,169	10,000,000
Balance at Dec. 31, 2018	$ 1,110		2,474,238	2,331,552	4,806,900
Balance (in shares) at Dec. 31, 2018	110,949,850
Increase (Decrease) in Shareholders' Equity
Net income					422,186
Balance at Sep. 30, 2019	$ 1,127	$ 100	2,758,928	2,702,018	5,462,173
Balance (in shares) at Sep. 30, 2019	112,701,349	10,000,000
Balance at Mar. 31, 2019	$ 1,111	$ 100	2,717,405	2,455,201	5,173,817
Balance (in shares) at Mar. 31, 2019	111,118,169	10,000,000
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon vesting of restricted stock units and upon exercise of options	$ 6		10,791		10,797
Issuance of common stock upon vesting of restricted stock units and upon exercise of options (in shares)	547,957
Issuance of preferred stock			(111)		(111)
Stock-based compensation			5,863		5,863
Dividends declared on preferred stock				(4,271)	(4,271)
Cash dividends (declared $0.10 and $0.13 per share of Class A common stock)				(14,516)	(14,516)
Net income				128,305	128,305
Balance at Jun. 30, 2019	$ 1,117	$ 100	2,733,948	2,564,719	5,299,884
Balance (in shares) at Jun. 30, 2019	111,666,126	10,000,000
Increase (Decrease) in Shareholders' Equity
Issuance of common stock upon vesting of restricted stock units and upon exercise of options	$ 11		20,584		20,595
Issuance of common stock upon vesting of restricted stock units and upon exercise of options (in shares)	1,047,695
Stock-based compensation			4,897		4,897
Dividends declared on preferred stock				(3,844)	(3,844)
Cash dividends (declared $0.10 and $0.13 per share of Class A common stock)				(14,644)	(14,644)
Tax withholding related to vesting of restricted stock units and exercise of stock options	$ (1)		(501)		(502)
Tax withholding related to vesting of restricted stock units and exercise of stock options (in shares)	(12,472)
Net income				155,787	155,787
Balance at Sep. 30, 2019	$ 1,127	$ 100	$ 2,758,928	$ 2,702,018	$ 5,462,173
Balance (in shares) at Sep. 30, 2019	112,701,349	10,000,000