CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Common Stock and Paid in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of reclassification of the instrument-specific credit risk portion of junior subordinated debentures fair value adjustments and reclassification of equity securities from available-for-sale	$ 0			$ (28,203)	$ 28,203
Balance, beginning of the period at Dec. 31, 2017	1,272,626		$ 1,187,127	90,535	(5,036)
Balance, beginning of the period (in shares) at Dec. 31, 2017		32,726,485
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	28,790			28,790
Other comprehensive income, net of income tax	(21,777)				(21,777)
Repurchase of common stock	(15,359)		(15,359)
Repurchase of common stock (in shares)		(269,711)
Accrual of dividends on common stock	(11,349)			(11,349)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	1,192		1,192
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(33,101)
Balance, end of the period at Mar. 31, 2018	1,254,123		1,172,960	79,773	1,390
Balance, end of the period (in shares) at Mar. 31, 2018		32,423,673
Balance, beginning of the period at Dec. 31, 2017	1,272,626		1,187,127	90,535	(5,036)
Balance, beginning of the period (in shares) at Dec. 31, 2017		32,726,485
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	98,987
Balance, end of the period at Sep. 30, 2018	1,272,198		1,175,250	109,942	(12,994)
Balance, end of the period (in shares) at Sep. 30, 2018		32,402,757
Balance, beginning of the period at Mar. 31, 2018	1,254,123		1,172,960	79,773	1,390
Balance, beginning of the period (in shares) at Mar. 31, 2018		32,423,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,424			32,424
Other comprehensive income, net of income tax	(6,521)				(6,521)
Accrual of dividends on common stock	(27,712)			(27,712)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	696		696
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(17,977)
Balance, end of the period at Jun. 30, 2018	1,253,010		1,173,656	84,485	(5,131)
Balance, end of the period (in shares) at Jun. 30, 2018		32,405,696
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,773			37,773
Other comprehensive income, net of income tax	(7,863)				(7,863)
Accrual of dividends on common stock	(12,316)			(12,316)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	1,594		1,594
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(2,939)
Balance, end of the period at Sep. 30, 2018	1,272,198		1,175,250	109,942	(12,994)
Balance, end of the period (in shares) at Sep. 30, 2018		32,402,757
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,527			37,527
Other comprehensive income, net of income tax	20,098				20,098
Repurchase of common stock	(19,042)		(19,042)
Repurchase of common stock (in shares)		(325,000)
Accrual of dividends on common stock	(13,414)			(13,414)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	1,519		1,519
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(3,056)
Business acquisition	179,709		179,709
Business acquisition (in shares)		3,108,071
Balance, end of the period at Dec. 31, 2018	1,478,595		1,337,436	134,055	7,104
Balance, end of the period (in shares) at Dec. 31, 2018		35,182,772
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	33,346			33,346
Other comprehensive income, net of income tax	12,790				12,790
Accrual of dividends on common stock	(14,490)			(14,490)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	950		950
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(30,026)
Balance, end of the period at Mar. 31, 2019	1,511,191		1,338,386	152,911	19,894
Balance, end of the period (in shares) at Mar. 31, 2019		35,152,746
Balance, beginning of the period at Dec. 31, 2018	1,478,595		1,337,436	134,055	7,104
Balance, beginning of the period (in shares) at Dec. 31, 2018		35,182,772
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	112,623
Balance, end of the period at Sep. 30, 2019	1,530,935		1,286,711	203,704	40,520
Balance, end of the period (in shares) at Sep. 30, 2019		34,173,357
Balance, beginning of the period at Mar. 31, 2019	1,511,191		1,338,386	152,911	19,894
Balance, beginning of the period (in shares) at Mar. 31, 2019		35,152,746
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	39,700			39,700
Other comprehensive income, net of income tax	16,016				16,016
Repurchase of common stock	(32,073)		(32,073)
Repurchase of common stock (in shares)		(600,000)
Accrual of dividends on common stock	(14,354)			(14,354)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	575		575
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		20,897
Balance, end of the period at Jun. 30, 2019	1,521,055		1,306,888	178,257	35,910
Balance, end of the period (in shares) at Jun. 30, 2019		34,573,643
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	39,577			39,577
Other comprehensive income, net of income tax	4,610				4,610
Repurchase of common stock	(21,849)		(21,849)
Repurchase of common stock (in shares)		(400,000)
Accrual of dividends on common stock	(14,130)			(14,130)
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered	1,672		1,672
Amortization of stock-based compensation related to restricted stock grants, net of shares surrendered (in shares)		(286)
Balance, end of the period at Sep. 30, 2019	$ 1,530,935		$ 1,286,711	$ 203,704	$ 40,520
Balance, end of the period (in shares) at Sep. 30, 2019		34,173,357