Deposits (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deposits [Abstract]
Interest-bearing Domestic Deposit, Brokered	$ 0	$ 0
Deposits, by Type [Abstract]
Non-interest bearing demand	1,791,364	1,491,683
Interest bearing:
Demand	2,133,273	1,848,806
Savings	1,843,355	1,602,544
Time, $100 and over	520,125	492,051
Time, other	718,095	698,666
Total interest bearing	5,214,848	4,642,067
Total deposits	7,006,212	6,133,750
Time deposits obtained through Certificate of Deposit Account Registry Service (CDARS)	40,491	51,526
Contractual Maturities, Time Deposits, $100,000 or More [Abstract]
2015, Time, $100 and Over	337,404
2016, Time, $100 and Over	90,509
2017, Time, $100 and Over	58,387
2018, Time, $100 and Over	20,971
2019, Time, $100 and Over	12,854
Thereafter, Time, $100 and Over	0
Time Deposits, $100,000 or More	520,125	492,051
Time Deposits, Fiscal Year Maturity [Abstract]
2015, Time	803,986
2016, Time	209,192
2017, Time	127,367
2018, Time	62,084
2019, Time	35,577
Thereafter, Time	14
Time Deposits	1,238,220
Interest expense, time deposits, $100,000 or more	4,003	4,880	6,951
Time Deposits, $250,000 or More	228,410	207,504
FDIC Deposit Insurance Limit	$ 250