Condensed Financial Information (Parent Company Only) - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed balance sheets:
Cash and cash equivalents	$ 758,986	$ 782,023
Investment in subsidiaries, at equity:
Other assets	145,747	81,705
Total assets	12,213,255	9,063,895
Subordinated debentures held by subsidiary trusts	82,477	82,477
Total liabilities	10,785,639	8,081,302
Stockholders’ equity	1,427,616	982,593	$ 950,493	$ 908,924
Total liabilities and stockholders’ equity	12,213,255	9,063,895
Parent Company
Condensed balance sheets:
Cash and cash equivalents	42,300	138,400
Investment in subsidiaries, at equity:
Equity method investments	1,432,300	932,000
Advances from subsidiaries, net	25,700	0
Other assets	61,700	35,400
Total assets	1,562,000	1,105,800
Other liabilities	51,900	18,000
Advances from subsidiaries, net	0	2,700
Long-term debt	0	20,000
Subordinated debentures held by subsidiary trusts	82,500	82,500
Total liabilities	134,400	123,200
Stockholders’ equity	1,427,600	982,600
Total liabilities and stockholders’ equity	1,562,000	1,105,800
Bank subsidiary | Parent Company
Investment in subsidiaries, at equity:
Equity method investments	$ 1,432,300	$ 932,000