Loans and Allowance for Loan Losses - Changes in the carrying value of acquired credit impaired loans - (Details)	3 Months Ended		12 Months Ended
	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Changes in the carrying amount of accretable difference for acquired impaired and non-impaired loans
Decline in accretable yield balance		$ 64,100,000	$ 46,200,000
Percentage of loss adjustment based on most current collateral value	90.00
Maximum
Changes in the carrying amount of accretable difference for acquired impaired and non-impaired loans
Threshold limit of loans for risk assessment by loan officers	$ 500,000			$ 500,000
Minimum
Changes in the carrying amount of accretable difference for acquired impaired and non-impaired loans
Threshold limit of loans for risk assessment by loan officers	100,000			100,000
Acquired credit impaired loans
Changes in the carrying value of acquired loans at the acquisition date
Balance at the beginning of the period		919,402,000	733,870,000	919,402,000	$ 1,220,638,000
Net reductions for payments, foreclosures, and accretion			(131,635,000)	(189,191,000)	(299,329,000)
Change in the allowance for loan losses on acquired loans			(311,000)	(3,659,000)	1,907,000
Balance at the end of the period	733,870,000		602,546,000	733,870,000	919,402,000
Changes in the carrying amount of accretable difference for acquired impaired and non-impaired loans
Balance at beginning of period		$ 306,826,000	201,538,000	306,826,000	301,516,000
Accretion			(72,757,000)	(97,847,000)	(105,254,000)
Reclass of nonaccretable difference due to improvement in expected cash flows			25,808,000	61,985,000	112,316,000
Other changes, net			790,000	(69,426,000)	(1,752,000)
Balance at end of period	$ 201,538,000		$ 155,379,000	$ 201,538,000	$ 306,826,000