Fair Value Measurements - (Table of Valuation Techniques and Unobservable Inputs Used in Valuation of Financial Instruments Falling Within Level 3 of Fair Value Hierarchy) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total assets at fair value	$ 994,238,000	$ 872,441,000
Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Prepayment speed	$ 8.7
Minimum | Impaired loans [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Appraised values Discount rate	0.00%
Minimum | Mortgage servicing rights member
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Appraised values Discount rate	9.50%
Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Prepayment speed	$ 11.3
Maximum | Impaired loans [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Appraised values Discount rate	25.00%
Maximum | Mortgage servicing rights member
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Appraised values Discount rate	10.50%