Condensed Financial Information (Parent Company Only) - Condensed Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed balance sheets:
Cash and cash equivalents	$ 798,670	$ 534,827
Investment in subsidiaries, at equity:
Other assets	73,495	61,056
Total assets	8,609,936	7,564,651
Subordinated debentures held by subsidiary trusts	82,477	82,477
Total liabilities	7,701,012	6,763,070
Stockholders’ equity	908,924	801,581	751,186	771,020
Total liabilities and stockholders’ equity	8,609,936	7,564,651
Parent Company
Condensed balance sheets:
Cash and cash equivalents	65,483	105,274
Investment in subsidiaries, at equity:
Equity method investments	938,799	795,872
Advances from subsidiaries, net	4,337	0
Other assets	29,335	26,809
Total assets	1,037,954	927,955
Other liabilities	26,553	17,602
Advances to subsidiaries, net	0	6,295
Long-term debt	20,000	20,000
Subordinated debentures held by subsidiary trusts	82,477	82,477
Total liabilities	129,030	126,374
Stockholders’ equity	908,924	801,581
Total liabilities and stockholders’ equity	1,037,954	927,955
Bank subsidiary
Investment in subsidiaries, at equity:
Equity method investments	936,817	793,892
Nonbank subsidiaries
Investment in subsidiaries, at equity:
Equity method investments	$ 1,982	$ 1,980