Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income	$ 73,917	$ 88,141	$ 77,969	$ 82,839	$ 71,891	$ 85,552	$ 71,436	$ 71,945	$ 322,866	$ 300,824	$ 197,063
Preferred stock dividends	2,437	2,438	2,437	2,438	2,437	2,438	2,437	2,438	9,750	9,750	9,750
Net income available to common stockholders	$ 71,480	$ 85,703	$ 75,532	$ 80,401	$ 69,454	$ 83,114	$ 68,999	$ 69,507	$ 313,116	$ 291,074	$ 187,313
Denominator:
Denominator for basic earnings per share—weighted average shares									50,286,300	49,936,702	49,587,169
Effect of employee stock-based awards									132,904	218,275	239,008
Effect of warrants to purchase common stock									0	117,895	433,657
Denominator for dilutive earnings per share—adjusted weighted average shares and assumed conversions									50,419,204	50,272,872	50,259,834
Basic earnings per common share	$ 1.42	$ 1.70	$ 1.50	$ 1.60	$ 1.38	$ 1.66	$ 1.39	$ 1.40	$ 6.23	$ 5.83	$ 3.78
Diluted earnings per common share	$ 1.42	$ 1.70	$ 1.50	$ 1.60	$ 1.38	$ 1.65	$ 1.38	$ 1.38	$ 6.21	$ 5.79	$ 3.73
Stock options excluded from computation of EPS									86,308	27,100	13,500